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Photodegradation of microplastics
Fotodegradación de microplásticos
Edgar Catarí
1
, Franklin Ramón Vargas
2
* & Beatriz Celeste Angulo
3
Received: 03/05/2023 – Received in revised form: 03/09/2023 – Accepted: 03/12/2023 –
Published: 19/03/2024
Research
Articles
X
Review
Articles
Essay
Articles
* Author for correspondence.
Abstract: The environmental degradation processes that plastics suffer in the environment are described, thus generating minor fragments known as
microplastics. The various chemical mechanisms by which these microplastics can be decomposed by the effect of light and environmental oxygen (photo-
oxidation of polymers) will be described. Emphasis is placed on the role of photochemistry in the degradation processes of microplastics until they become
compounds that are harmless to the environment, that is, until they are mineralized (HCO
3
, CO
2
, etc.). Some advances in the development of heterogeneous
photocatalysts based on transition metals used in the degradation of microplastics are also presented, including a particular and interesting automated microrobot
photocatalyst system based on BiVO
4
/Fe
3
O
4
, which has proven to be effective. in the degradation of polylactic acid (PLA), polycaprolactone (PCL), polyethylene
terephthalate (PET) and polypropylene (PP) microplastics on a laboratory scale.
Key words: Photodegradation, microplastics, photochemistry, polymere, photooxidation.
Resumen: Se describen los procesos de degradación ambiental que sufren los plásticos en el medio ambiente generando así fragmentos de menor tamaño,
conocidos como microplásticos. Se describirán los diversos mecanismos químicos mediante los cuales éstos microplásticos se pueden descomponer por efecto
de la luz y el oxígeno ambiental (fotooxidación de polímeros). Se hace énfasis en el rol de la fotoquímica en los procesos de degradación de los microplásticos
hasta transtornarlos en compuestos inofensivos para el ambiente, es decir, hasta llevarlos a su mineralización (HCO
3
, CO
2
, etc.). Se presentan además algunos
avances en el desarrollo de fotocatalizadores heterogéneos basados en metales de transición, empleados en la degradación de los microplásticos, incluyendo un
particular e interesante sistema de fotocatalizador microrobot autómata basado en BiVO
4
/Fe
3
O
4
, el cual ha demostrado ser efectivo en la degradación de
microplásticos de poliácido láctico (PLA), policaprolactona (PCL), ereftalato de polietileno t (PET) y polipropileno (PP) a escala de laboratorio.
Palabras claves: Fotodegradación, microplásticos, fotoquímica, polímeros, fotooxidación.
1. Introduction
Today, plastics are one of the most versatile materials used
by humans, their two main components being a polymer
matrix (macromolecules) and a certain number of additives
(UV protectants, plasticizers, colorants, other polymers,
etc.). The first fully synthetic polymer was obtained in the
early 20th century by Leo Baekeland, however, the real
beginning of the industrial production of polymers occurred
in the early 1950s, since then the manufacture of polymers
has grown exponentially reaching 380 metric tons per year
(2015) [1]. Most of the polymers produced in the world are
of the thermoplastic type, these types of materials are low
cost, their raw materials are from non-renewable sources
(petroleum) and they are commonly identified simply as
"plastics". Among these plastics we have polyethylene (PE),
polyethylene terephthalate (PET), high, low and linear-low
density polyethylene (HDPE, LDPE and LLDPE),
polyvinyl chloride (PVC), polypropylene (PP),
polycarbonate (PC), polystyrene (PS), etc. [2-5].
Plastics have enabled the development and evolution of
several technological areas, for example, automotive,
electronics, food, medicine, aerospace, shipping, clothing,
1
Laboratorio de Polímeros, Centro de Química “Dr. Gabriel Chuchani” Instituto Venezolano de Investigaciones Científicas – IVIC.
https://orcid.org/00000-0002-6558-9237 , ecatari@gmail.com ; Caracas; Venezuela.
2
Laboratorio de Fotoquímica, Centro de Química “Dr. Gabriel Chuchani” Instituto Venezolano de Investigaciones Científicas – IVIC.
https://orcid.org/0000-0001-8170-7793 , vargas2212@gmail.com ; Caracas; Venezuela.
3
Laboratorio de Biogeoquímica, Centro de Ciencias Atmosféricas y Biogeoquímica, Instituto Venezolano de Investigaciones Científicas –
IVIC. https://orcid.org/0000-0002-7138-7797 , angulobcs@gmail.com ; Caracas; Venezuela
footwear, construction, etc. Most used plastics are very
durable due to their chemical and biological inertness,
which is the result of their high molecular mass,
hydrophobicity and absence of functional chemical groups
susceptible to attack by microbes, enzymes, light, water,
etc. [6, 7]. The high durability, inertness and impermeability
of plastics make them ideal materials for food packaging,
sterile medical devices, the construction sector, among
others, however, these characteristics also make plastics
particularly long-lived when discarded after their useful life.
Certain additives incorporated into plastics, such as
antioxidants and stabilizers, increase the shelf life of these
materials by reducing the rate of degradation in natural
environments [6-9].
The high durability, inertness and impermeability of plastics
make them ideal materials for food packaging, sterile
medical devices, the construction sector, among others,
however, these characteristics also make plastics
particularly long-lived when discarded after their useful life.
Certain additives incorporated into plastics, such as
antioxidants and stabilizers, increase the shelf life of these
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materials by reducing their degradation rate in natural
environments [6-9].
According to the Organization for Economic Co-operation
and Development (OECD) [10], currently, more than
100,000 different chemical substances and compounds are
marketed worldwide, including various types of plastics.
Many of these plastics, after their use or useful life, end up
deposited in natural systems (land, water and air), where
they slowly begin to biodegrade through diverse and
complex chemical and biological processes that in many
cases are initiated or activated by the participation of solar
energy. To understand how these processes of photo-
degradation of plastics occur, photochemistry provides the
basic concepts that adequately describe them, and more
specifically the photo-oxidation reactions of polymers allow
plausible explanations of these photo-degradation processes
[5, 11, 12].
Post-consumer plastics can be degraded by the following
pathways: (1) photo-oxidation, (2) thermal, (3) ozone-
induced, (4) mechano-chemical, (5) catalytic and (6)
biodegradation. In turn, the degradation rate of plastics
depends on their chemical composition, molecular mass,
hydrophobic character, presence of functional groups,
additives, types of bonds present in the main polymer chain,
method of polymer synthesis, polymer morphology,
environmental conditions where the plastic is placed, size
and shape of the plastic part [13].
During the degradation of plastics, these materials undergo
fragmentation and consequently a reduction in their
dimensions, reaching micro (0.1-5000 μm) and nanometric
(1-100 nm) sizes [12]. Nowadays, several studies have
found micro/nanoplastics in seas, rivers, oceans, even on
mountain tops, and even in the internal organs of many
living organisms, surprisingly there is evidence of the
presence of micro/nanoplastics in human placenta [14].
Micro/nanoplastics present in seas and oceans can be
ingested by organisms as small as zooplankton and
transferred to larger animal species, such as fish, when these
zooplankton are ingested by them. Various toxic substances
present in the environment can adhere to the surface of
micro/nanoplastics and are then ingested and transported by
living organisms.
The use of photocatalysts to accelerate the degradation of
plastics is shown to be an efficient way to reduce the amount
of these environmental pollutants. Photocatalysis uses a
renewable and inexhaustible energy source such as sunlight.
Additionally, the degradation of plastics, induced by photo-
catalysts, can generate intermediate products of lower
molecular mass that in some cases can be used as raw
material for the chemical industry, organic synthesis and in
the production of new chemical products and even new
plastics [15].
This chapter provides an overview of the various photo-
degradation processes of plastics in the presence of oxygen,
their reaction mechanisms, the factors governing their
reaction rates and some photo-catalytic systems currently
being investigated for the degradation of micro/nanoplastics
present in the environment.
Plastics and their impact on the environment
Plastics are materials based on polymeric matrices
homogeneously mixed with various types of additives such
as: colorants, antioxidants, plasticizers, silica, carbon black,
calcium sulfate, calcium carbonate, talc, etc. The use of
plastics dates to the 19th century with the discovery of the
vulcanization reaction of natural rubber by Charles
Goodyear [4, 16]. Polymers can be of natural or synthetic
origin; the latter being manufactured from chemical
compounds of low molecular mass and of fossil origin
(petroleum) called monomers. In a synthetic polymer, these
monomers are joined together by covalent bonds forming
long macromolecular chains of very diverse shapes and
chemical compositions. The first synthetic polymers were
developed during the 19th century, while the 20th century
saw the development of a great diversity of polymeric
materials, see Table 1:
Table 1. Timeline of plastics development [4].
The first synthetic polymer was synthesized in 1907:
Bakelite, followed by the industrial development of
polyvinyl chloride or PVC in 1926, followed by
polyurethane (PUR) (1937), polystyrene (1938), high-
density polyethylene (HDPE) and polypropylene (PP)
(1951). Recent technological advances have led to the
development of polymers from bacterial fermentation of
sugars and lipids. These materials obtained from natural
sources are called biopolymers and include
polyhydroxyalkanoates (PHA), poly (lactic acid) (PLA),
aliphatic polyesters and polysaccharides [4]. Polymers of
natural origin, such as poly(isoprene) (natural rubber), are
used for the manufacture of vulcanized rubber used in the
manufacture of tires; another biopolymer, poly (lactic acid),
is used as a material for food packaging, blister packs or
sutures in the medical and pharmaceutical sectors, in 3D
printing, etc. [17]. In general, synthetic or natural polymers
can be classified into: (i) thermoplastics: materials that can
be molded into virtually any desired shape through thermal
processes such as rotational molding, injection molding,
extrusion, compression molding, blow molding or
thermoforming. (ii) elastomers: are materials that have
macromolecular chains linked together by bridges and
crosslinking points randomly located, this particular
macromolecular structure allows elastomers can be
deformed without breaking under external forces, and then
when this effort ceases the material returns to its original
size and shape, these elastomeric materials are commonly
referred to as rubbers or rubbers, (iii) thermosets: are
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materials whose macromolecules are joined together by
multiple molecular bridges whose chemical composition
may or may not be different from that of the main
macromolecular chain, these materials are mostly rigid
solids very resistant to heat, once formed thermosetting
polymers can not be melted again [9, 18, 19].
As of 2015, global demand for polymers was 388 million
tons of which 99.5% were petroleum-based polymers and
only the remaining 0.5% were biopolymers [20].
Polypropylene (PP) accounted for 16% of global demand,
while low-density polyethylene (LDPE) accounted for 12%,
poly (vinyl chloride) (PVC) for 11%, high-density
polyethylene (HDPE) for 10%, polyethylene terephthalate
(PET) for 5%, polystyrene (PS) for 5%, other
thermoplastics for 3%, non-pneumatic elastomers for 2%
and thermosetting polymers for 9% [20]. The uses of
plastics are very diverse; Table 2 summarizes some of the
applications of the main commercial polymers.
Table 2. Applications of the most popular commercial
polymers [4].
Once plastics have completed their useful life, they are
discarded by companies, commercial establishments,
hospitals, homes and other places. Plastic waste can become
a major environmental problem due to the absence of
policies and/or strategies for the collection, sorting and
reuse of plastic waste. Significant amounts of plastic waste
can end up in municipal landfills, in the sea or on the ground
where it remains indefinitely. Another way in which post-
consumer plastics are introduced into the environment is
through mechanical erosion. This process generates fine
plastic particles that can be transported long distances by air
or water; examples of this form of plastic particle generation
are the wear and tear of tires during vehicle rolling, or the
turning of plastic parts, among others. The way in which
plastics are transported and deposited in the environment
will depend on the geographic location of the source, the
type of activity that generates plastic waste and the
existence or absence of adequate infrastructure to collect
and process these materials. For example, municipal
landfills that lack adequate urban sanitary infrastructure are
identified as a major source of plastic waste generation into
the environment. An example of plastic pollutants
intentionally placed in urban drains is the microscopic PE
beads contained in facial scrubs; these plastic particles are
probably present more frequently in developed countries
where these types of products are massively used. In
general, obtaining accurate data on the sources of plastic
wastes present in different ecosystems is hampered by the
difficulty in determining the length of time that these wastes
have remained in bodies of water (oceans, seas, rivers, etc.)
and on land [11, 16, 18, 21].
Meteorization of plastics in natural environments
Plastic waste is considered dangerous for the environment
due to its capacity to remain for a long time in large bodies
of water (rivers, seas, oceans), these wastes can fragment
into small pieces and be ingested by living organisms
causing their suffocation and/or intoxication. The presence
of this plastic waste represents a global environmental threat
with harmful consequences for ecosystems and living
beings. Potentially, the chemical decomposition of plastics
can generate toxic compounds, such as polychlorinated
biphenyls, bisphenol A, flame retardants, perfluorinated,
phthalates, bisphenols, nonylphenols, among others, Figure
1 [15].
After post-consumer plastics are discarded, part of them are
discharged into the environment, these plastics undergo
physical, chemical and biological weathering processes
which involves a slow decomposition of the large plastic
pieces obtaining microplastics and nanoplastics in the
process [11, 22-24]. Microplastics can be classified into
primary and secondary.
Primary microplastics are those microscopic plastics
manufactured for industrial or domestic use, for example,
microparticles of polyethylene terephthalate (PET),
polyethylene (PE) or polymethyl methacrylate (PMMA) are
dispersed in cosmetic products such as toothpastes, body
creams, shampoos, scrubs, sunburn creams, makeup and
hygiene products, to increase the abrasive effect and
improve their performance. Other products such as baby
wipes, make-up removers, among others, use polyester
(PES), polyethylene (PE) and polypropylene (PP)
microparticles. Once these industrial and domestic products
are used, the plastic microparticles contained in them are
released into the wash water, becoming an environmental
liability. In addition, large quantities of primary
microplastics are generated by the abrasion of car tires
during driving, as well as during the washing of synthetic
textiles [25]. Microplastics have become a global problem,
since 2010 microplastics have been detected in more than
200 species of edible animal species (164 marine fish, 23
mollusks, 7 crustaceans, 2 birds, 2 freshwater fish, 2 turtles,
chicken), some food products (canned sardines, salt, sugar
and honey), as well as in beer and water [15, 26].
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Figure 1. Some toxic compounds generated by chemical
decomposition of plastics, (i) polychlorinated biphenyls, (ii)
biphenol A, (iii) phthalates and (iv) nonylphenol.
Primary microparticles loose in the environment can
undergo degradation processes causing their fragmentation
and generating secondary microplastics. These are more
reactive and hazardous to marine fauna and living beings
than primary microplastics. Secondary microplastics are
generated from the wear and tear of fishing nets, industrial
resin granules, household items and other types of plastic
waste. Various environmental and chemical factors control
the levels of fragmentation (degradation) of plastics,
therefore, depending on the degradation mechanism that
these materials undergo, we can classify these degradation
processes into:
(i) biodegradation (action of living organisms), (ii) photo-
degradation (light radiation), (iii) thermo-oxidative
degradation (slow oxidative decomposition at moderate
temperature), (iv) thermal degradation (high temperature),
(v) hydrolysis (reaction with water) [15, 26, 27].
Regardless of the degradation process that the plastics
undergo, the degradation products that are generated are
incorporated into the environment (water, soil, air), thus
increasing the concentration and variety of dissolved
organic species. This varied chemical environment in turn
creates the right conditions for new degradation processes
to take place until the polymer macromolecules reach their
mineralization (formation of inorganic species in CO2,
H2O, N2, H2, CH4, HCO3- salts and minerals).
Upon reaching seas and oceans, microplastics are
distributed according to their buoyancy, which is
determined by their density and surface interaction
(wettability). Today there is an enormous amount of post-
consumer plastic in the sea, and the formation of plastic
islands up to 3 km in length and areas of the seabed with
high concentrations of submerged plastic of up to 1.9
million pieces/m
2
have been reported. As the size of the
plastic particle decreases, they can be ingested by
microalgae or marine invertebrates, causing their
intoxication and even their death, which is why
microplastics have been identified as agents that increase
the ecotoxicity of the environment and affect the food chain
[11]. Plastic weathering occurs due to many different
processes and causes alterations in the chemical properties
of the contaminants generated by the plastic [22].
The effects of weathering of plastics on the environment
include the accelerated release of plasticizers and toxic
additives. Weathering and its consequences on plastics are:
(1) fragmentation of larger plastic debris thereby increasing
the specific surface area; (2) modulation of polymer
properties (e.g., crystallinity); (3) oxygen-containing
functional groups change the surface properties of
microplastics by decreasing their hydrophobicity; and (4)
biofilms attached on microplastics increase their toxin
adsorption capacity [15].
Photochemical degradation of plastics
Photochemical reactions basically occur as a result of the
activation of a molecule from its fundamental state (S0) to
an electronically excited state called singlet (S*) and/or
triplet (T*), this electronic transition occurs due to the
absorption of a photon (light). If this energetic transition
occurs without a change of electronic spin in the molecule,
the excited electronic state that is reached is called singlet
(S1), in the case that the molecule absorbs higher energies
at the appropriate frequencies, then higher singlet excited
states can be reached (S2, S3, .., Si) [31]. When the
electronic transition, caused by the absorption of a photon,
produces a change of the electronic spin in the molecule
(unpaired of two electronic spins), the excited state obtained
is called triplet (T1), moreover, if the absorbed energy is
high enough, higher triplet energy states (T2, T3, ..., Ti) can
be reached.
When the degradation reaction of a polymer takes place in
a radiation-free environment (hv), under an inert
atmosphere (vacuum, nitrogen or argon) and without the
intervention of other mechanisms such as mechanical or
biological, the only changes in the microstructure of the
material that occur are chain breaking and cross-linking. On
the other hand, when the degradation process of a polymer
takes place in the presence of light and under an oxidizing
environment (air, oxygen), photo-oxidative degradation of
the material occurs. In the photo-oxidative degradation of
almost all polymers, the following steps can be considered
[9, 19]:
Photoinitiation
Polymers (PH) may contain intramolecular impurities such
as certain chromophore groups (light absorbing functional
groups), such as: C=O, C=C, ROOH and/or external light
absorbing (RR') impurities (intermolecular impurities),
such as: traces of catalyst, solvent, additives, atmospheric
pollutants, metal particles, etc. These impurities can
generate polymeric radicals (P) and hydroperoxide (HO
2
.-)
in the presence of air (oxygen) and under the effects of
UV/VIS (visible) radiation, the general reaction scheme for
the formation of these radicals is shown below. [19]:
(Radical of external impurity)
(Polymeric radical)
When light acts on the intramolecular impurities in the
polymer described above, chain fragmentation and the
formation of radicals of various sizes (R: methyl, ethyl, etc.)
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occur, the extent of this type of reaction will depend on
other factors associated with the properties of the material.
(Polymer radical formation)
A very common contaminant found in polymers is catalyst
residues, which can generate radicals that initiate polymer
degradation reactions. Many commercial polymers contain
residues of metallic compounds and certain amounts of
additives that are deliberately incorporated into the material,
including the presence of particles and metallic traces may
be due to mechanical wear suffered by the different
production systems of these polymers (reactor walls, blades,
pipes, etc.). Catalysts based on transition metals such as
titanium or zirconium are widely used in the synthesis of PE
and PP. After polymer synthesis, residues of these transition
metals can remain occluded in the material in
concentrations of around 2-100 ppm. These metal residues
are associated with thermal stability and photo-degradation
problems in plastics.
The generation of photosensitizing agents is initiated by the
absorption of a photon of light (hv) by TiO
2
and the
promotion of an electron of the transition metal from its
valence band (BV) to its conduction band (BC), thus
forming a positive hole-electron pair.
The relative proportion of reactive species formed in
photosensitization will depend on the presence of water and
oxygen in the reaction system, therefore, TiO
2
will not
promote photosensitization without the presence of oxygen
and water. Table 3 below shows some photo-initiating
compounds for polymer photo-degradation reactions:
Table 3. Various photo-initiators to accelerate the
degradation of different polymers.
In turn, photon radiation can catalyze the formation of
charge transfer complexes (CTC) between ambient oxygen
and the polymer (PHO
2
), these types of complexes are very
unstable and generally decompose easily generating
polymer radicals and hydroperoxides:
Chain propagation.
Chain propagation is the reaction where a peroxide radical
group (POO) is inserted into the main polymer chain,
starting from a polymer radical and atmospheric oxygen:
(Formation of peroxide polymeric radical)
This reaction is very fast and leads to the formation of
polymer hydroperoxides (POOH) and radicals (P) from
hydrogen abstraction from a polymer chain (PH):
POO∙ + PH → P∙ + POOH
(Hydroperoxide polymer formation)
The abstraction of hydrogen atoms from polymer chains,
promoted by peroxide radicals (POO.), occurs preferentially
on the tertiary carbons of the chain, however, it has been
reported that this abstraction of hydrogens can also occur on
secondary carbons [19].
The abstraction of hydrogen atoms during chain extension
can also occur intramolecularly, for which there must be a
favorable stereochemical arrangement between the
peroxide group (POO.) and the hydrogen atom to be
abstracted.
In addition to promoting the formation of polymer radicals
(P.), radical peroxides (POO) participate in the termination
reactions, which compete with chain propagation, forming
in the process polymer peroxides (POOP), polymer ethers
(POP) and release in the process of molecular oxygen [31].
Norrish Type I and II Reactions
Polymers containing oxygenated groups of the ketone type
can undergo two types of photochemical reactions:
a) Norrish type I (radical) reaction, also known as -
scission reaction, generates radicals (P.) and carbon
monoxide (CO), Figure 2.
Figure 2. Norrish type I reaction
b) Type II Norrish reaction (non-radical), this type of chain
cleavage involves the abstraction of intermolecular
hydrogen by a six-membered cyclic intermediate which
undergoes a rearrangement resulting in a ketone group on
the polymer chain and a short chain olefin, Figure 3.
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Figure 3. Norrish type II reaction
Type I and II Norrish reactions depend on the structure of
the polymer, for example, the type I Norris chain-breaking
reaction in ethylene and carbon monoxide polymers occurs
in very low yield, since this type of polymers possesses a
strong cage effect (solvent protection) and high reactivity of
the primary radicals produced in the reaction. On the other
hand, the Norrish type II reaction in ethylene-carbon
monoxide copolymers do not occur due to the absence of -
hydrogens.
Due to the rapid diffusion of the small acetyl radical (CH
3
-
Ċ=O), away from the newly formed radical (P), this
situation increases the effectiveness of Norrish type I
photolysis. The Norrish type II reaction depends on the
lifetime of the triplet excited state, furthermore this excited
species must be stable enough to allow cyclic rearrangement
of the chain, which can be a six- or seven-membered
intermediate. Six-membered cyclic intermediates are
formed in phenyl vinyl ketone polymers (PPVK), while
seven-membered cyclic intermediates are produced in
methyl methacrylate-methyl vinyl ketone copolymers
(MVK-MMA).
The development of Norrish type II photoscission of
macromolecules differs significantly from the photoscission
of small molecules. The diffusion of small molecules
partially controls the energy transfer process, whereas in a
polymeric medium the migration of excitation energy
depends entirely on the viscosity of the macromolecule. In
macromolecules, the development of type I and type II
Norrish reactions is very limited when performed below the
glass transition temperature of the polymer (Tg), since at
this temperature there is no significant molecular motion,
while above Tg, the quantum yields of Norrish reactions in
polymers are almost identical to the reactions performed in
solution at the same temperature (increased molecular
mobility) [19].
Photo-degradation of chlorinated polymers.
Dehydrochlorination is the most characteristic reaction of
chlorinated polymers such as PVC during UV radiation, this
reaction leads to the formation of unsaturated chain sections
(-CH=CH-)n in the polymer, n can vary from 2 to 13. These
dehydrochlorination reactions are responsible for the
appearance of a yellow-red coloration in PVC. In addition
to the dehydrochlorination reactions, PVC, when subjected
to UV irradiation (hv) in the presence of water and
humidity, can undergo typical photooxidation reactions
with the formation of carbonyl groups, carboxylic acids,
hydroxides and hydroperoxides, as already described in
previous sections. In the specific case of chlorinated
polyvinyl chloride (CPVC), its photo-dehydrochlorination
induces the formation of chlorinated polyene sequences.
Polymers obtained from CPVC dehydrochlorination can be
completely dehydrochlorinated when laser radiation is used,
thus generating graphene structures.
Photo-degradation of polymers induced by dyes or
dyestuffs.
Virtually all commercial plastic materials contain dyes or
colorants in their composition. Dye-induced photo-
degradation is a phenomenon commonly found in various
industrial sectors, such as land, air and sea transportation,
construction, electronics, and many others.
A dye molecule (D) is able to absorb light and become
energetically activated until it reaches a singlet (1D) and/or
triplet (3D) excited state (we will denote both excited states
as D*).
The photoactivated dye molecule (D*) can then abstract a
hydrogen atom from the polymer (PH) and produce a radical
(P) together with a hydrogenated dye radical (DH). In the
presence of water (moisture) and molecular oxygen, or in
the case of the use of wet dyes, the photoactivated dye
molecules can generate hydroxyl radicals (HO.) and
hydroperoxides (HOO.) and a hydrogenated radical species
of the initial dye itself (DH.).
The hydroxyl (HO) and hydroperoxide (HO
2
) radicals are
very reactive and rapidly abstract hydrogen atoms from the
polymer (PH) thus generating radicals (P) that can
subsequently undergo photooxidation reactions, as
described in the previous section.
Inactivation of this photoactive dye molecule (D*) can
generate a semi-oxidized radical cation (D
+
) or a semi-
reduced radical anion (D
-
).
The disproportionation reaction of the two dye ions (D
-
y
D
+
),
leads to the regeneration of two dye molecules:
Both dye radicals can also participate in the following
reactions:
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The radical anion of the dye (D
-
) often has a strong
tendency to take a proton from the environment and/or
establish chemical equilibrium with it.
Both D.- and DH. species represent semi-reduced forms of
the dye molecule in the ground state (S0), the dye radical
DH. is a very reactive species and generates a colorless
product (DH
2
) known as the leucoform of the dye derived
from its disproportionation reaction:
This leucoform can also be formed from the abstraction of
a hydrogen atom from the polymer:
In an oxygenated medium the dye radical DH. produces an
oxygen radical ion. (O2.-).
In the presence of water, an electron (e-) can be solvated
generating a species (eac-) that can react with the
surrounding molecular oxygen and water.
Electron solvation
Oxygen radical ion formation
Hydroperoxide radical and hydroxide anion
Hydrogen peroxide
Hydroperoxide radical anion
Hydrogen peroxide and hydroxide anion
Hydrogen peroxide formation
Another reaction that can occur is the transfer of energy
between the excited dye molecule and molecular oxygen,
thus forming singlet oxygen (1O2):
D* (T1) + O
2
------- D (S0) +
1
O
2
Singlet oxygen formation
Table 4 below shows various types of dyes commonly used
in the plastics industry that produce singlet oxygen (
1
O
2
) by
energy transfer, the energies of their triplet states (ET) are
in the range of 30-56 kcal mol-1.
Table 4. Dyes that promote photodegradation of plastics
[31]
All of these dye photoinitiation reactions can cause
discoloration of dyes contained in plastics. The mechanisms
of dye discoloration are complex and often depend on the
structure of the dye and the chemical and/or physical nature
of the polymer. Dye photosensitization deterioration of
plastics occurs when a dye accelerates the breakdown of the
molecular structure of a polymer, all in the presence of
molecular oxygen and water. The degree of photo-
degradation of plastics due to dyes can be decreased by the
addition of stabilizers [33].
Photocatalytic degradation of plastics
Photocatalytic degradation of plastic can be described as the
whole set of reactions that polymer chains undergo,
promoted by a photosensitizing catalyst, resulting in the
decomposition or degradation of the polymer together with
the generation of gases, minerals, monomers, oligomers and
other different chemicals [34]. The diffusion of reactive
species through the polymer matrix increases its
macromolecular degradation, among the reactions that
occur are oxidation, chain breaking and crosslinking
reactions.
Plastics are difficult to degrade due to their poor water
solubility, high structural stability and non-biodegradable
character. Photocatalysis has proven to be an effective
method for plastic degradation. Photosensitization is the
process in which a chemical species absorbs a photon of
light in the presence of water and/or oxygen, and forms
reactive species in the process, such as hydroxyl radical
(HO.) and superoxide (HOO.), these species initiate the
degradation of the plastic through chain breaking reactions,
branching, crosslinking and finally the mineralization of the
polymer in the form of H
2
O, CO
2
and other compounds.
Some studies of photocatalytic degradation of plastics are
shown in Table 5 below [35].
For a catalyst to be active in the photo-degradation of
plastics, it must consist of a semiconducting metal that
absorbs radiant energy or light (hv), thus becoming a
photosensitizing species that accelerates the rate of plastic
degradation. An ideal photocatalyst should absorb light at
room temperature, be highly stable to photo-corrosion and
at the same time be non-toxic to the environment and living
beings. The effectiveness of a photocatalyst depends on its
oxidation-reduction potential. In this sense, the oxidation-
reduction potentials of various compounds used as
photocatalysts in the degradation of plastics are shown
below. The values of the normal oxidation potential are
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referenced to the normal oxidation potential of hydrogen
[36].
If a photocatalyst (semiconductor) has a valence band
maximum (VBM) more positive than 1.23 eV (of O
2
/H
2
O),
it means that its oxidation capacity is sufficient to promote
water oxidation, therefore, as the VBM value of a given
photocatalyst is more positive it means that the oxidation
capacity of that photocatalyst will be higher. An order in
oxidation capacity of some studied photocatalysts follows
the following trend: ZnS > ZnO - TiO
2
> WO
3
> CdS.
On the contrary, if the semiconductor exhibits a minimum
conduction band more negative than the normal hydrogen
reduction potential, it means that the photocatalyst will then
be able to promote the reduction of water, and the higher the
value of that conduction band, the higher the reduction
capacity of the photocatalyst. (ZnS - CdS - CdSe > ZnO >
TiO
2
- Si) [36].
One of the most widely used photocatalysts in the
degradation reaction of plastics is TiO
2
, which has a high
oxidation-reduction potential, high chemical and thermal
stability, low cost and is environmentally friendly (non-
toxic). On the other hand, zinc oxide (ZnO) has a band gap
similar to TiO
2
and is often used as an alternative to TiO
2
.
Other semiconductors used as photocatalysts in the
degradation of plastics are: iron oxide (Fe2O3), cadmium
sulfide (CdS), zinc sulfide (ZnS), tungsten oxide (WO
3
), tin
oxide (SnO), bismuth vanadate (BiVO
4
), and non-metallic
carbon nitrides (N
3
C
4
) [36]. Table 5 below shows a
summary of the different heterogeneous photocatalytic
systems that have been studied in the degradation of various
types of plastics.
Tabla 6. Photocatalytic degradation studies of various types
of plastics [35].
Autonomous photocatalytic microbots for microplastics
degradation
One of the important characteristics that a photocatalyst
must possess is a large surface area, however, classical
synthesis methods of heterogeneous photocatalysts involve
physical deposition processes under constant agitation,
these types of synthesis methods are expensive and do not
generate particles small enough to achieve a large surface
area per gram of material. Additionally, most photocatalysts
are toxic and cannot be reused after their use in the plastic
photo-degradation reaction.
In 2021, Pumera et al., [37] reported the synthesis of novel
automaton photocatalytic systems called by their creators as
microrobots based on bismuth vanadate (BiVO4), these
heterogeneous photocatalysts are able to move through
aquatic environments in an automaton way, use low energy
and interact with microplastics in the environment to
subsequently photo-degrade them inside their structure.
These swimming microrobots can be driven by magnetic
fields, electric fields, ultrasound and ambient light, in
addition, these microrobots contain iron oxide (Fe3O4)
which allows the recovery of the microrobots from the
reaction medium by using a magnet. The highlights of this
particular photocatalytic system are as follows:
I. Adequate potential bandgap.
II. A low recombination speed of the load torque.
III. An asymmetric physical shape.
IV. Easy interaction with visible light.
V. Photoreaction with the water in the medium generates
disproportionately shaped products, which promotes
their movement (automaton).
The BiVO4/Fe3O4 microrobots were housed in the host
tunnel along with a certain amount of microplastics, initially
the microrobots were not in contact with the microplastics,
subsequently the experiment is initiated by allowing the
microrobots to move along the host tunnel while sunlight is
applied to the system. The light promotes photoreactions in
the microrobots allowing the microrobots to move until they
absorb onto the surface of the microplastics. To confirm the
adhesion strength of the microrobots on the microplastics, a
magnetic field (magnet) is applied to the system to separate
the microplastics with attached microrobots from the
microplastics without attached microrobots [37]. The
adhesion of microrobots on the surface of microplastics is
attributed to adsorption/precipitation mechanisms
previously observed in the anchoring of heavy metals and
organic pollutants on oceanic microplastics.
The microrobots use H
2
O
2
as fuel to asymmetrically
generate products such as H+ and O
2
, the formation of these
products drives the microrobots in aqueous media causing
them to contact the microplastics thus initiating
microplastic degradation reactions. The photodegradation
reactions of microplastics involve the formation of free
radicals, breaking of C-C and/or N-C and C-O bonds,
among other reactions that occur simultaneously.
This study succeeded in demonstrating that the
photocatalytic automaton microrobots are able to efficiently
degrade different types of microplastics, in particular
polylactic acid (PLA), polycaprolactone (PCL), due to their
automaton movement capability which allows an effective
interaction between the microplastics and the photocatalyst
without the need of using external mechanical stirrers.
These photocatalytic automaton microrobots have
demonstrated for the first time that it is possible to
efficiently photo-degrade plastic microparticles in complex
confined spaces, which can significantly boost research on
environmental microplastic treatments in order to reduce
the amount of these pollutants in the environment.
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Conclusions
In the last 20 years, the detection of microplastics in aquatic
and terrestrial environments and in the air has set off alarm
bells in the scientific and industrial sectors; the harmful
effects of these micrometric materials on the health of living
beings have been scientifically corroborated. Therefore,
important projects have been initiated around the world to
study this artificial phenomenon in order to minimize its
effects on the planet's ecosystems and living beings.
Photochemistry provides the conceptual tools necessary to
understand and develop technological strategies by which it
would be possible to break down microplastics to the extent
of harmless mineral compounds. The photo-degradation
reactions of plastics depend mostly on the presence of
water, sunlight, imperfections and/or contaminants in the
plastic and also on the chemical composition of the polymer
to be degraded.
The times of photo-degradation reactions of plastics are
very long, so the use of heterogeneous photocatalysts to
accelerate these photo-degradation processes constitutes a
technology strategy with great potential for success to be
considered in the future. Great advances have been made in
the development of photocatalysts for the degradation of
microplastics, it is estimated that within a few decades we
will be in the presence of the emergence of important
technologies for environmental decontamination of
microplastics, and photocatalysis will undoubtedly play a
leading role in the purification of seas, rivers and even the
air and land of our planet.
References
[1] Chamas, A., Moon, H., Zheng, J., Qiu, Y., Tabassum, T., Jang,
J., Abu-Omar, M., Scot,t S., Suh, S. ACS Sustainable Chemistry
Engineering vol. 8, pp. 3494-3511, 2020.
[2] Gewert, B., Plassmann, M., Macleod, M. Environmental
Science Processes & Impact Vol. s17(9), pp. 1513-1521, 2015.
[3] Sen, S. K., Raut, S. Journal Environmental Chemical
Engineering vol. 3, pp.462-473, 2015.
[4] Lambert, S. Environmental Risk of Polymer and their
Degradation Products pp. 1-198, 2013.
[5] Webb, H., Arnott, J., Crawford, R., Ivanova, E. Polymers. vol.
5, pp. 1-18, 2013.
[6] Yousif, E., Haddad, R. Springerplus. vol. 2, pp. 1-32, 2013.
[7] Niaounakis, M. Management Mar Plastic Debris. pp. 127-142,
2017
[8] Daglen, B. C, Tyler, D. R. Green Chemistry Letters and
Reviews. vol. 3, pp. 69-82, 2010.
[9] Rabek, J. F. in Photodegradation of Polymers, Springer Berlin
Heidelberg, Berlin, Heidelberg pp. 51-97. 1996.
[10] OECD Environment Directorate. 168, 2021.
[11] Andrady, A. Marine Pollution Bulletin. vol. 62(8), pp. 1596–
1605, 2011.
[12] Auta, H. S., Emenike, C., Fauziah, S. Environment
International. Vol. 102, pp. 165-176, 2017.
[13] Singh, B., Sharma, N. (2008) Polymer Degradation and
Stability. vol. 93(3), pp. 561-584, 2008.
[14] Ragusa, A., Svelato, A., Santacroce, C., Catalano, P.,
Notarstefano, V., Carnevali, O., Papa, F., Rongioletti, M. C. A.,
Baiocco, F., Draghi, S., D’Amore, E., Rinaldo, D., Matta, M.,
Giorgini, E. Plasticenta: Microplastics in human placenta,
bioRxiv, DOI:10.1101/2020.07.15.198325. 2020.
[15] Bratovcic, A. Journal of Nanosciience & Nanotechnology
Applications. vol. 3, pp. 304-312, 2019.
[16] Crawford CB & B Quinn (2017) Microplastic pollutants.
Amsterdam, Netherlands. Elsevier, 336.
[17] Doble M & A Kumar (2005) in Biotreatment of industrial
effluents, eds. M. Doble and A. Kumar. 101-110.
[18] Webb, H. K., Arnott, J., Crawford, R. J., Ivanova, E. P. Plastic
degradation and its environmental implications with special
reference to poly(ethylene terephthalate), Polymers (Basel). vol. 5,
pp. 1-18, 2013
[19] Rabek, J. F. (1995) in Polymer Photodegradation, Chapman
& Hill.
[20] Ryberg, M. W., Laurent, A., Hauschild, M. Mapping of global
plastics value chain. Vol. 96, 2018.
[21] Fotopoulou, K. N., Karapanagioti, K. K. Degradation of
Various Plastics in the Environment, Handbook Environmental
Chemistry vol. 78, pp. 71-92, 2019.
[22] Pickett, J. R. Weathering of plastics, Elsevier Inc., Third Edit,
2018.
[23] Fabiyi J.S. & A.G. Mcdonald (2014) Maderas, Ciencia y
Tecnología. 16:275–290.
[24] Lambert, S., Sinclair, C. J., Bradley, E. L, Boxall, A. B.
Science Total Environmental. Vol. 447, p.p. 225-234, 2013.
[25] Crawford, C. B., Quinn, B. Microplastic pollutants.
Amsterdam, Netherlands. Elsevier, pp. 336, 2017.
[26] Wetherbee, G., Baldwin, A., Ranville, J. It is raining plastic.:
U.S. Geological Survey Open-File Report. p.p. 1048, 2019.
Disponible en https://pubs.er.usgs.gov/publication/ofr20191048
26//2020.
[27] Klein S, Dimzon I, Eubeler J & T Knepper (2018) Analysis,
Occurrence, and Degradation of Microplastics in the Aqueous
Environment. In: Wagner M., Lambert S. (eds) Freshwater
Microplastics. The Handbook of Environmental Chemistry
Springer, Cham, 58:302.
[28] Menéndez-Pedriza, J. Interaction of environmental pollutants
with microplastics: A critical review of sorption factors,
bioaccumulation and ecotoxicological effects, 2020.
DOI:10.3390/TOXICS8020040.
[29] Fotopoulou, K. N., Karapanagioti, H. K. in Hazardous
Chemicals Associated with Plastics in the Marine Environment,
Springer International Publishing AG, 2017.
[30] Canopoli, L., Coulon, F., Wagland, S. T. Science Total
Environmental vol. 698, pp. 134125, 2020
[31] Rabek, J. F. Photodegradation of Polymers, Springer
International Publishing, Berlin, Heidelberg, 1996.
[32] Niki, E., Yamamoto, Y., Kamiya, Y. Oxidative Degradation
of Polymers. vol. III, pp. 78-95, 1978.
[33] Rabek, J. F. Polymer Photodegradation. pp. 24–66, 1995.
[34] Malhotra, S. K., Pisharody, L., Karim, A. V. Journal of
Materials Research. vol. 99, pp. 163-178, 2021.
[35] Ouyang, Z., Yang, Y., Zhang, C., Zhu, S., Qin, L., Wang, W.,
He, D., Zhou, Y., Luo, H., Qin, F. Journal of Materials Chemicals
A. vol. 9, pp. 13402-13441, 2021.
[36] Lee, Q. Y, Li, H. Photocatalytic degradation of plastic waste:
A mini review, Micromachines, 2021. DOI:10.3390/mi12080907.
[37] Beladi-Mousavi, S. M., Hermanová, S., Ying, Y., Plutnar, J.,
Pumera, M. ACS Applied Materials & Interfaces. 2021.
DOI:10.1021/acsami.1c04559.
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Table 1. Timeline of plastics development [4].
XIX Century
XX Century
Year/Polymer
Developer
Year/Polymer
Developer
1839/ Natural Rubber Latex
Charles Goodyear
1909/Bakelite
Leo Hendrik Baekeland
1839/ Polystyrene
Edward Simon
1926/Plasticized PVC
Walter Semon
1862/Parkesina
Alexander Parkes
1933/ Poly (vinylidene chloride)
Ralph Wiley
1865/ Cellulose Acetate
Paul Schützanberger
1935/Low density polyethylene
Reginald Gibson and Eric
Fawcett
1869/Celluloid
Jhon Wesley Hyatt
1936/Poli (metil metacrilato)
Reginald Gibson and Eric
Fawcett
1872/ Poly(vinyl chloride)
Eugen Baumann
1937/Polyurethanes
Otto Bayer
1894/ Viscous rayon
Charles Frederick Cross
1938/Polystyrene
Commercially made
1938/Polyethylene Terephthalate
John Whinfield and James
Dickson
1942/Unsaturated Polyester
John Whinfield and James
Dickson
1951/Polypropylene
Paul Hogan and Robert Banks
1953/Polycarbonate
Hermann Schnell
1954/Polystyrene foam
Ray McIntire
1960/Poly (lactic acid)
Patrick Gruber
1978/Linear low density
polyethylene
DuPont
Table 2. Applications of the most popular commercial polymers [4].
Polymer Type
Uses and applications
Polyethylene (PE)
Low-density PE: compressible bottles, toys, carrier bags, electrical
insulation, chemical tank liners, heavy-duty sacks, general packaging,
gas and water pipes.
High-density PE: chemical drums, toys, picnic items, household and
kitchen items, cable insulation, carrier bags and food wrapping
material.
Polypropylene (PP)
Food packaging, microwave food trays and in the automotive
industry.
Poly (vinyl chloride) (PVC)
Construction, transportation, packaging, electrical/electronic and
sanitary applications.
Polyethylene Terephthalate (PET)
Beverage bottles, cable liner for baking trays.
C
C
H
H
H
H
n
C
C
H
H
H
CH
3
n
C
C
H
H
H
Cl
n
O
C
O
C
O
O C C
H
H
H
H
n
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Pag. 13
Polystyrene (PS)
Food packaging, take-out boxes, beverage cups, plastic cutlery,
protective packaging and CD cases.
Polyurethane (PU)
Printing rollers, solid tires, wheels, shoe heels, automotive bumpers,
as foams in mattresses and car seats, and in biomedical applications.
Polycarbonate (PC)
Bottles, utensils, containers, foils, electrical items and medical
applications.
Poly(methylpentene) (PMP)
Medical articles, syringes, lamp covers (good heat resistance), radar
applications, encapsulation and microwave food packaging.
Polytetrafluoroethylene (PTFE)
Anti-stick coating, gaskets, bearings, high and low temperature
medical and electrical applications, laboratory equipment, pump parts
and thread sealing tape.
Poli(Sulfuro de fenileno) (PPS)
Sterilizable electrical, automotive, kitchen, medical, dental and
laboratory equipment, hair dryer racks and components.
Polyisoprene (NR)
Gloves, tires, rubber boots, rubber bands, pencil erasers, hoses, belts,
flooring and medical applications.
Acrylonitrile-butadiene-styrene (ABS)
Piping, musical instruments, golf club heads, automobiles, medical
devices for blood access, electrical devices, protective helmets,
whitewater canoes, small kitchen appliances and toys.
C
C
H
H
H
n
C
N
C
n
H
H
N
O
H
C O C C
H
O
O
H
H
H
H
O
C
n
CH
3
CH
3
O C
O
C
C
H
H
H
CH
2
n
CH
H
3
C CH
3
C
C
F
F
F
F
n
S
n
H
2
C
n
C C
CH
2
H CH
3
C
C
H
C C
CH
2
C C
H
H
m
H
H
CN
CH
2
H H
n
H
o
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Pag. 14
Polybutadiene
Tires, golf balls and inner tubes.
Styrene-Butadiene (SBR)
Tires, footwear, construction and paper coating applications
Poly(hydroxyalkanoate) (PHA)
Medical devices, such as cardiovascular patches, orthopedic pins,
adhesion barriers, stents, guided tissue repair/regeneration devices,
articular cartilage repair devices, bone implant material, drug delivery
system, tissue engineering scaffolding, loading and filling agents.
Table 3. Various photo-initiators to accelerate the degradation of different polymers
Photo-initiator
Fragmentation reaction
Polymer
Acetophenone
derivative
PE, EPDM B
Benzoin derivatives
PE, PMMA, PVC, PS
Chloronitroso
compounds
PI
Benzophenone
PE, PP, PS, PEP,
PVAP, PEG, CA PAMS, PBD,
EPDM B, PNR,
Quinones
PE, PP, PVC, PS, PA, Cellulose
H
2
C
n
C C
CH
2
H H
CH
2
C C
CH
2
C C
H
H
CH
2
H H
m
H
n
n
H
O
O
OH
CH
3
C
O
C
OR
OR'
H
hv
C
O
C
OR
OR'
H
+
C
O
C
OR
R'
hv
C
O
C
OR
R'
+
hv
+
C
R Cl
NOR
C
R
NOR
Cl
C
O
hv
+
PH
C
OH
+
P
hv
+
PH
+
P
O
O
O
OH
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Ingeniería Química
Ingeniería Química y Desarrollo
Universidad de Guayaquil | Facultad de Ingeniería Química | Telf. +593 4229 2949 | Guayaquil – Ecuador
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Pag. 15
Note: EPDM B: ethylene-propylene-diene rubber type B, PE: polyethylene, PMMA: polymethylmethacrylate, PVC: polyvinyl
chloride, PS: polystyrene, PI: poly(isoprene), PEP: Poly(ethylene-co-propylene), PVAP: poly(vinyl acetophenone), PEG:
poly(ethylene glycol), PAMS: poly( -methylstyrene), PBD: polybutadiene, PNR: polynorbornene, CA: cellulose, PA:
polyamide.
Table 4. Dyes that promote photo degradation of plastics [31]
Dye
Triplet energy (E
T
)
(kcal mol
-1
)
Fluorescein
47,2
2,7- Dichlorofluorescein
46,0
Eosin Y
45,5
Rose Bengal
42,0
O
COO
-
O
-
O
O
COO
-
O
-
O
ClCl
O
COO
-
O
-
O
BrBr
Br Br
O
COO
-
O
-
O
II
I I
Cl
Universidad de
Guayaquil
Ingeniería Química y Desarrollo
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ISSN – p: 1390 –9428 / ISSN – e: 3028-8533 / INQUIDE / Vol. 06 / Nº 01
Facultad de
Ingeniería Química
Ingeniería Química y Desarrollo
Universidad de Guayaquil | Facultad de Ingeniería Química | Telf. +593 4229 2949 | Guayaquil – Ecuador
https://revistas.ug.edu.ec/index.php/iqd
Email: inquide@ug.edu.ec | francisco.duquea@ug.edu.ec
Pag. 16
Rhodamine B
43,0
Rhodamine 6G
42,0
Sulforhodamine B
41,8
Acriflavin
51,1
Proflavine
51,1
Acridine Orange
O
COOH
NHC
2
H
5
(C
2
H
5
)
2
N
O
COOH
NHC
2
H
5
(C
2
H
5
)
2
N
O
SO
3
-
NHC
2
H
5
(C
2
H
5
)
2
N
SO
3
H
N NH
2
H
2
N
CH
3
N NH
2
H
2
N
H
N N(CH
3
)
2
(H
3
C)
2
N
H
Universidad de
Guayaquil
Ingeniería Química y Desarrollo
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ISSN – p: 1390 –9428 / ISSN – e: 3028-8533 / INQUIDE / Vol. 06 / Nº 01
Facultad de
Ingeniería Química
Ingeniería Química y Desarrollo
Universidad de Guayaquil | Facultad de Ingeniería Química | Telf. +593 4229 2949 | Guayaquil – Ecuador
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Email: inquide@ug.edu.ec | francisco.duquea@ug.edu.ec
Pag. 17
Methylene blue
32,0
Lumichrome
55,4
Lumiflavin
50,5
Crystal violet
42,0
Riboflavin
50,0
N
S N(CH
3
)
2
(H
3
C)
2
N
N
N
N
N
HH
3
C
O
O
H
H
3
C
N
N
N
N
HH
3
C
O
O
CH
3
H
3
C
C
NH
2
H
2
N
H
3
C
N
N
N
N
HH
3
C
O
O
CH
2
H
3
C
CH
CH
HO
HO
CHHO
H
2
C OH
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Pag. 18
Table 5. Photocatalytic degradation studies of various types of plastics. [35].
Polymer /
Photocatalyst
Experimental details
Experimental results
LDPE/ZnO microplastic
wastes
A 50 W dichroic halogen lamp in air was
used as a visible light source ( 60–70 klux);
175 hours of illumination; 1 x 1 cm size
films of LDPE and 20 mM ZnO
The carbonyl index (CI) and vinyl index (VI) showed an increase
of 30%; new functional groups such as hydroperoxide carbonyl
and unsaturated groups were formed during photodegradation,
cracks and stains were observed on the LDPE film after
photodegradation.
Micro plastic of LDPE /
Pt/ZnO
A 50 W dichroic halogen lamp in air
generated visible light (60–70 klux); 175
hours of illumination; a commercial PELD
film with a thickness of 50 microns and
dimensions of 2.5 x 0.75 cm was evaluated;
ZnO-Pt substrates with an average diameter
and length of 960 m were used as
photocatalyst.
VI and IC increased by 15% and 13%, respectively; various
cracks, wrinkles and cavities of different sizes were detected in
all photodegraded films, and volatile organic compounds and
oxygenated groups were formed.
Micro plastic HDPE / C,
N-TiO
2
200 mg of microplastics and 200 mg of the
photocatalyst were added to 50 ml of a
buffer solution for 50 h of continuous
stirring at 300 rpm; a 50 W LED lamp was
employed as a visible light source.
Low temperature and pH have a combined effect on microplastic
degradation. At pH = 3 and 0°C, the mass loss after 50 h of
irradiation was 71%; the degradation rate constant, k = 0.0237
HDPE micro plastic / N-
TiO
2
A 27W fluorescent lamp was used as a
constant light source in the visible light
spectrum for 20 hours at room temperature.
The first order kinetic constant was 12.2x10
-4
h
-1
(solid medium)
and 38.2 h
-1
(aqueous medium).
PE micro plastic /
hydroxide-rich BiOCl
ultra thin film
A water circulation system under a 250 W
Xe lamp; 1 g.L
-1
micrometer grade plastic
(PE-S) or 10 g.L-
1
of millimeter grade
plastic were dispersed in 100 mL of an
aqueous solution; 1 g.L
-1
of
photocatalyst was added.
PE microplastics photo-degraded by BiOCl-1 showed a mass
loss of 5.38%, which was 134 and 24 times higher than the
degradation obtained with light alone (0.04%) and BiOCl/light
(0.22%).
PE and PP / ZrO
2
, TiO
2
Degradation was evaluated under a sun
simulator and under real sunlight for 20
hours; PE and PP films of size 1.5 x 1.5 cm;
ZrO
2
, TiO
2
photocatalyst at 10 000 ppm.
The CIs of the original PE and PP were 0.0090 and 0.0072,
respectively. The average CIs of PE and PP treated with ZrO
2
,
under a sun simulator and under real sunlight, were 0.0244,
0.0382, 0.0149 and 0.0190, respectively. Under real sunlight
were 0.0244, 0.0382, 0.0149 and 0.0190, respectively. The
average CIs of PE and PP treated with TiO
2
, under sun simulator
and under real sunlight were 0.0226, 0.0260, 0.0112 and 0.0124
respectively. ZrO
2
cause higher photocatalytic effect on the
polymers.
PLA, PET and PUR /
CdS/CdO
x
CdS of 0.5 M irradiated for 4 h at 25°C
with simulated sunlight (AM 1.5 G, 100 mW
cm
-2
); solution volume was 2 ml of 10M
NaOH in a sealed photo-reactor (internal
volume of 7.91 mL) under anaerobic
conditions; 50 mg mL
-1
PLA, 25 mg mL
-1
PET, 25 mg mL
-1
PUR.
Photo-reforming of PUR, PET and PLA generated H
2
with
activities of 0.85, 3.42 and 64.3 mmol H
2
g.CdS
-1
h
-1
,
respectively. PLA in NaOH(ac) hydrolyzed to sodium lactate,
which was oxidized forming an alkaline-induced pyruvate-based
compound. PET was hydrolyzed to terephthalate, ethylene
glycol and isophthalate, while its photooxidation produced
formate, glycolate, ethanol, acetate and lactate. PUR first
hydrolyzed to aliphatic and aromatic components, where the
aromatic component remained intact during photo-reforming,
while the aliphatic component was photo-oxidized to pyruvate,
acetate, formate and lactate.
PE and PVC / Pt/TiO
2
500 W Xe lamp, 10 h of irradiation; 300 mg
Pt/TiO
2
; 150 mg PE and PVC, 30 ml of
deionized water
Photo-reforming of PE and PVC generated H
2
with activities of
0.015 and 0.031 mmol H2 g.cat
-1
h
-1
in 5 M NaOH.
PET /MoS
2
/Cd
x
Zn
1-x
S
10 mg of MoS
2
/Cd
x
Zn
1-x
S; 60 mL of PET
substrate solution; a 300 W Xe lamp with
AM 1.5G was used as light source; under
anaerobic conditions.
4.3 wt.% de MoS
2
in MoS
2
/Cd
x
Zn
1-x
S exhibited the best H
2
evolution rate of 15.90 mmol.g
-1
.h
-1
. PET was finally oxidized to
small molecule organic compounds, such as methanol, formate,
ethanol and acetate.
Universidad de
Guayaquil
Ingeniería Química y Desarrollo
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ISSN – p: 1390 –9428 / ISSN – e: 3028-8533 / INQUIDE / Vol. 06 / Nº 01
Facultad de
Ingeniería Química
Ingeniería Química y Desarrollo
Universidad de Guayaquil | Facultad de Ingeniería Química | Telf. +593 4229 2949 | Guayaquil – Ecuador
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Email: inquide@ug.edu.ec | francisco.duquea@ug.edu.ec
Pag. 19
PP, PEBD/ NiAl
2
O
4
A 350 W metal halide lamp; a PP film of size
3 x 3 cm; 30 mg NiAl2O4; DMSO as solvent
(20 mL); a 3x3 cm PP film; 30 mg NiAl
2
O
4
;
DMSO as solvent (20 mL).
The weight loss of PP, LDPE was 12.5% and 10% respectively
with NiAl2O4 (prepared via hydrothermal synthesis) and
NiAl
2
O
4
(prepared via co-precipitation) respectively.
PE and PLA / CN
x
/Ni
2
P
2 wt% (3.2 mg) ultrasonicated CN
x
/Ni
2
P, 50
mg polymer, KOH(ac) (1M or 10M, 2 mL),
sealed photo-reactor (internal volume 7.91
mL); anaerobic conditions, simulated
sunlight (AM 1.5G, 100 mW cm
-2
, 25°C).
H
2
conversion reached 6.7% for PLA and 24.5% for PET at
higher pH (KOH, 10 M).
(KOH, 10 M); the results showed that H
2
was generated
continuously for 6 consecutive days, the photocatalytic activity
reached 4.13 mmol H
2
g.CdS
-1
h
-1
, the conversion was 5.15%
and the external quantum yield was 2.17% in the degradation of
real-world PET water bottles. The PET hydrolyzed to its
monomers (ethylene glycol and terephthalate) or soluble
oligomer fragments. PLA hydrolyzed to lactate during
pretreatment, and then oxidized mainly to CO
3
-2
and small
amounts of acetate, formate and other unidentified products.
