Approximately 70% of global municipal solid waste is lost to landfills or the environment each year, an emblem of our increasingly unsustainable economic system in which materials and energy are, Lignocellulose is Earths most abundant form of biomass and its valorization to H2 is a key objective for the generation of renewable fuels. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Photodegradation Performance of g-C3N4 Fabricated by Directly Heating Melamine. Ultraviolet radiation consists of electromagnetic waves with a wavelength between 100 and 400 nm [12], which is further divided into three major sub-regions. Photocatalytic Conversion of Waste Plastics into C2 Fuels under ; Liu, D.Q. Many of those plastics produced in 1950 still exist as plastic waste in the environment. Photocatalytic Conversion of Plastic Waste: From Photodegradation to Yousif, E.; Haddad, R. Photodegradation and photostabilization of polymers, especially polystyrene: Review. (b) Surface photovoltage spectroscopy spectra of TiO2 and TiO2/CuPc photocatalyst. Photocatalytic valorization directly utilizes solar energy to transform plastic pollutant into . The Design of TiO, Park, H.; Park, Y.; Kim, W.; Choi, W. Surface modification of TiO, Finazzi, E.; Di Valentin, C.; Pacchioni, G.; Selloni, A. As a result, anatase has a relatively higher photocatalytic activity, however, a relatively narrower absorption bandwidth. Statements. TiO2 is the most widely used photocatalyst due to its versatile properties such as high level of oxidation-reduction ability [21,22], chemical stability [21], high-temperature stability, cost-effectiveness, and environmental friendliness [23,24]. Maeda, K.; Domen, K. Photocatalytic Water Splitting: Recent Progress and Future Challenges. Photobiol. Green and red balls represent Ti and O atoms, respectively. ; Li, J.H. Borysiewicz, M.A. Therefore, a multifunctional photocatalyst that consists of individual elements working for a specific plastic could be very useful for addressing the plastic waste issue. Photocatalytic Degradation of Plastic Waste: A Mini Review Plastic waste becomes an immediate threat to our society with ever-increasing negative impacts on our environment and health by entering our food chain. Thus, a photocatalyst that could degrade these contaminations should be developed and used together with the plastic degradation photocatalyst. Visit our dedicated information section to learn more about MDPI. Additionally, the widespread plastic waste makes collection and transportation necessary for centralized recycling technology such as mechanical and thermal catalytic recycling. Likewise, the singlet oxygen produced also leads to the formation of ROOH by the oxidation of an olefin containing allylic hydrogen, as depicted in Figure 2b. The photogenerated electrons are transferred from VC to the conduction band of TiO2 to form the superoxide radicals, according to Equation (3). Senasu T., Hemavibool K., Nanan S. Hydrothermally grown CdS nanoparticles for photodegradation of anionic azo dyes under UV-visible light irradiation. Hence, hydroxyl radical is known as the essential element in photocatalysis. The authors declare no conflict of interest. Yan S.C., Li Z.S., Zou Z.G. One can see that, after 500-h of illumination, PP30Ti and PPDTi show a very rough surface with very large cavities. Catalytic oxidation of polystyrene to aromatic oxygenates over a Aragaw T.A. Yong R.Y., Li J.H., Chen L.L., Liu D.Q., Li H.Z., Zheng Y., Ding J. Synthesis, surface modification and photocatalytic property of ZnO nanoparticles. A Norrish reaction can be subdivided into type I and type II reactions, and Norrish Type II reaction causes intermolecular rearrangement of the carbonyl group (C=O) to form the vinyl group (-CH=CH, The free radical mechanism of oxidation involves producing free radicals that react with the oxygen. Visible range photocatalysts for solid phase photocatalytic degradation of polyethylene and polyvinyl chloride. Joana Lia Ferreira, an assistant professor of conservation and restoration at the NOVA School of Science and Technology, recalls an exhibit with a lamp that had a black polyurethane foam shade. According to data from Plastic Europe, the most produced plastic type is polyolefin including high-density polyethylene (HDPE), low-density polyethylene (LDPE), and PP, which are mainly used in the packaging industry. PET and HDPE show a recovery rate of 19.5% and 10%, respectively, as depicted in Table 1. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (. Guo, Y.; Clark, S.J. In this perspective, we highlight the effect of photocatalytic approaches toward the. Zhao X., Li Z., Chen Y., Shi L., Zhu Y. Enhancement of photocatalytic degradation of polyethylene plastic with CuPc modified TiO, Fa W., Yang C., Gong C., Peng T., Zan L. Enhanced photodegradation efficiency of polyethylene-TiO, Asghar W., Qazi I.A., Ilyas H., Khan A.A., Awan M.A., Aslam M.R. However, an intensive research effort may be necessary for developing such a photocatalyst. Structure of (c) s-triazine and (d) tri-s-triazine as the primary building blocks of graphitic carbon nitride with C atoms in grey and N atoms in blue [50]; reprinted from [50] with permission from Elsevier. TiO2 with mixed crystalline forms (anatase and rutile) exhibits the highest activity for photodegradation of PP [(C3H6)n, as depicted in the inset of Figure 12a] with high consumption of oxygen [67]. Singlet oxygen mechanism of oxidation involves the direct reaction of singlet oxygen with polymer. Bhattacharjee A., Ahmaruzzaman M., Sinha T. A novel approach for the synthesis of SnO. To this end, photodegradation is perfect as sunlight is known to be an effective energy source to degrade plastic. articles published under an open access Creative Common CC BY license, any part of the article may be reused without Editors Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. The potential sources for producing free radicals are carbonyl groups such as ketones and hydroperoxides. Purple dotted box: Initiation step; black dashed boxes: Propagation step; orange dash-dotted boxes: Termination step. Photocatalytic conversion of waste plastics to low carbon number organic products - ScienceDirect Chinese Journal of Catalysis Volume 43, Issue 3, March 2022, Pages 589-594 Perspective Photocatalytic conversion of waste plastics to low carbon number organic products Kaiyi Su a b , Huifang Liu a , Chaofeng Zhang a , Feng Wang a Add to Mendeley Furthermore, due to the different molecular structures, it is found that the degradation of PS-TiO2/CuPc was slower than PE-TiO2/CuPc. In this review,. ; Chen, L.L. Thus, a key to increase the recycling rate of plastic waste, and thus less disposal of plastic waste to landfill, is to develop a decentralized degradation process that could leverage renewable energies as the driving force. Different phases have different symmetries of the octahedral-shaped TiO6 fundamental building blocks [28]. Put together, TiO2 has a great balance between oxidation-reduction capability and band gap size, resulting in an excellent photocatalyst. Gupta, A.; Lakshmp, Y.N. ; Ilyas, H.; Khan, A.A.; Awan, M.A. Zhang K., Hamidian A.H., Tubi A., Zhang Y., Fang J.K.H., Wu C., Lam P.K.S. Photocatalytic degradation of Naproxen and methylene blue: Comparison between ZnO, TiO. The outer layer of the mask can be made of polyethylene terephthalate (PET). Energy Source Part A Recovery Util. Shi H., Magaye R., Castranova V., Zhao J. Titanium dioxide nanoparticles: A review of current toxicological data. Subsequent reactions of polymer peroxyl radicals with another polymer produce hydroperoxides and polymer macro radicals (Path 3). ZnO as a Functional Material, a Review. Biomol. Contamination-tolerant degradation technology. Photocatalytic Degradation of Plastic Waste: A Mini Review ; Oasmaa, A.; Pihkola, H.; Deviatkin, I.; Tenhunen, A.; Mannila, J.; Minkkinen, H.; Pohjakallio, M.; Laine-Ylijoki, J. Pyrolysis of plastic waste: Opportunities and challenges. In the oxidative reaction, holes in the VB of photocatalyst react with the water in the air to form proton and hydroxyl radicals, as depicted in Equation (5). When the photocatalytic degradation of PS plastic was carried out with FePc-TiO2, HADPG-TiO2 or TiO2/CuPc as photocatalyst, it was found that these modified TiO2 had a widened absorption under visible light. Liang, Y.; Tan, Q.; Song, Q.; Li, J. Consequently, hydroxyl radicals will decompose organic pollutants into the water and carbon dioxide. Micromachines 2021, 12, 907. Interestingly, photocatalytic degradation of PVC film with the vitamin-C (VC)-modified TiO2 photocatalyst was investigated [61]. This research was funded by Singapore Ministry of Education under grant Tier 1 RG101/18 (grant number: 2018-T1-001-051). Three types of samples were prepared by mixing carbon-coated TiO2 and PP with the decreasing carbon content from PP5Ti (30.6 wt%), PP10Ti (11.6 wt%), PP30Ti (2.7 wt%) to PPDTi (0 wt.%), with reference to pure PP. Find support for a specific problem in the support section of our website. Most of the studied catalyst generates CO. Facile processes to introduce photocatalyst into plastic waste. Hence, polymers that are continuously exposed to UV radiation will undergo deterioration in their physical and chemical structure, resulting in photodegradation. The GGA+U approach is improved in terms of the energy gap of material and impurity state in the gap. Briefly, upon illumination, the photogenerated electrons and holes in TiO2 cause reduction and oxidation reactions, respectively, leading to the formation of ROSs. Thereafter, a generated singlet oxygen that reacts with the vinyl group could then further decompose the molecule, leading to chain scission and formation of hydroperoxides functional group (ROOH), as shown in Figure 2a. Conclusively, olefins and ketones are the expected products of the termination reactions [16]. Hence, hydroxyl radical is known as the essential element in photocatalysis. ; Morales-Garca, A.; Taravillo, M. DFT+U calculations of crystal lattice, electronic structure, and phase stability under pressure of TiO, Pan, X.; Yang, M.; Fu, X.; Zhang, N.; Xu, Y. redox potentials. and H.L. Photoelectrochemical conversion of plastic waste into high-value Photocatalytic degradation of polypropylene film using TiO. Rao, H.; Lu, Z.; Liu, X.; Ge, H.; Zhang, Z.; Zou, P.; He, H.; Wang, Y. Conversion of "Waste Plastic" into Photocatalytic Nanofoams for We use cookies on our website to ensure you get the best experience. instance of. C Photochem. Environ. However, the hazard of discarding waste plastic, so-called "white pollution", is becoming more and more severe. The free radicals then react with the oxygen to create the hydroxyl group (O-H) and carbonyl group (C=O). This mini review begins with an introduction to the chemical compositions of the common plastic waste. Rajaambal, S.; Sivaranjani, K.; Gopinath, C.S. Most of the UV-B is also absorbed by the atmosphere, while UV-A is completely reachable to the Earths surface. Singh B., Sharma N. Mechanistic implications of plastic degradation. The hydroxyl radicals produced will extract hydrogen from another polymer to form polymer macro radicals and water (Path 8). (A) Keyword clouds were generated to provide a correlation between most researched processes and plastic types. In photocatalytic degradation, which is a photochemical reaction process with the help of photocatalysts, a semiconductor is often used to absorb light and to accelerate the photoreaction rate [17]. However, an intensive research effort may be necessary for developing such a photocatalyst. Please let us know what you think of our products and services. Chemical recycling of waste plastics for new materials production. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Iron oxide [43], cadmium sulphide [44], zinc sulphide [45], tungsten oxide [46], tin oxide [47], bismuth vanadate [48], and non-metallic carbon nitride [49,50] are also often employed as the photocatalysts for photodegradation too, as depicted in Figure 7bd. Ohtani B., Adzuma S., Miyadzu H., Nishimoto S., Kagiya T. Photocatalytic degradation of polypropylene film by dispersed titanium dioxide particles. On top of that, more environmental issues have emerged, especially when there is a lack of proper management and handling of plastic wastes. The first step is degradation of plastics into CO 2, which is reduced in a second step to C 2 fuels over the same . Considering the low economic viability of such a process, a new method to introduce photocatalyst into plastic waste is needed. Cromer, D.T. The high rate of degradation was attributed to (1) rGO extending the absorption range of TiO2 to a visible region due to the presence of Ti-O-C bond; (2) rGO acting as a good electron acceptor thanks to its 2D -conjugation, facilitating electron-hole separation, and thus decreasing the recombination rate; and (3) rGO offering more adsorption sites and catalytic sites. Photobiol. Though the photocatalytic process shows good tolerance to these contaminations, it is a surface reaction. Very often, a plastic product consists of various plastic components, e.g., electronic plastic may contain polyimide, ABS, etc. Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. When the oxygen pressure is high, polymer peroxyl radicals react with themselves to form inert products and oxygen (Path 10). Plastic polymers including PE (LDPE, HDPE), PP, PS, and PVC are described in our review as they constitute the worlds most common plastic and most of them are challenging to be recycled. To increase the photocatalytic degradation activity under visible light, the energy band gap needs to be reduced. The recycling rate of plastic waste is very low (~10%) mainly caused by the contamination of plastic waste by other solid waste, as well as the fact that the mixing nature of plastic waste consists of various polymers. Focus of this review on catalytic photodegradation for various types of plastic polymers. In contrast, when sufficient oxygen cannot be maintained, polymer peroxyl radicals react with polymer macro radicals (Path 11). However, this deficiency can be corrected by the GGA+U approach with more appropriate determined U parameter values [36]. Meng X., Wang H., Qian Z., Gao X., Yi Q., Zhang S., Yang M. Preparation of photodegradable polypropylene/clay composites based on nanoscaled TiO, Kamrannejad M.M., Hasanzadeh A., Nosoudi N., Mai L., Babaluo A.A. Photocatalytic degradation of polypropylene/TiO, Verma R., Singh S., Dalai M.K., Saravanan M., Agrawal V.V., Srivastava A.K. Moreover, it is regarded that the interfacial charge transfer at the surface of the semiconductor is important in producing hydroxyl radicals, affecting the overall photocatalytic degradation rate [, Since UV light only represents 58% of the solar spectrum (at sea level), it limits the efficiency of photocatalytic degradation for most photocatalysts such as TiO, The photocatalytic degradation of PS plastic [(C, Investigations have been also carried out to determine the photocatalytic degradation efficiency of pure PVC [(C, Interestingly, photocatalytic degradation of PVC film with the vitamin-C (VC)-modified TiO, Compared with the abovementioned photocatalysts including TiO, The photocatalytic degradation rate of PE (see inset of, Fa et al. The author furthers characterized the photovoltage using surface photovoltage spectroscopy (SPS), as depicted in Figure 15b. 1 reference. Chatterjee D., Dasgupta S. Visible light induced photocatalytic degradation of organic pollutants. The aim is to provide a snapshot of some of the 2M pre-prints), Content across 9.5M topics & 32K+ academic journals. A structural investigation of titanium dioxide photocatalysts. The detailed energy band structure and density of state (DOS) of anatase and rutile TiO2 are similar, as shown in Figure 6 [27]. Moreover, other plastic wastes have also caused a variety of environmental issues, directly imposing an immediate threat to our health and survival. PVC has a recovery rate of 0%, suggesting that it is completely non-recyclable which is mainly due to the high chlorine content in its raw material and the high level of hazardous additives in it. In addition, the recent COVID-19 outbreak worldwide has caused a surge in the demand for medical personal protective equipment (PPEs) such as single-use disposable face masks, medical face shields, and gloves, most of which are made of polymer materials [4]. ; Aroua, M.K. PET and HDPE show a recovery rate of 19.5% and 10%, respectively, as depicted in, Therefore, engineering plastic degradation processes such as photodegradation [, Herein, we revisit the concept of catalytic photodegradation of plastic wastes. (b) The proposed mechanism of photocatalysis process for VC modified TiO2. Moreover, the TiO2/CuPc sample displays a broader range of photo response. From the experimental results, modified TiO2 photocatalysts showed a much higher photocatalytic degradation efficiency than pure TiO2. Iron oxide nanocatalyst with titanium and silver nanoparticles: Synthesis, characterization and photocatalytic activity on the degradation of Rhodamine B dye. Samples with increasing mass ratio of TiO2-OMT photocatalyst in the clay from 2, 5, and 10 mmol Ti/g clay were prepared as PP/OMTTi2, PP/OMTTi5, and PP/OMTTi10, respectively. The roles of TiO2 photocatalyst in the photodegradation process were then elaborated, followed by the recent advances of photocatalytic degradation of various plastic waste. New understanding of the difference of photocatalytic activity among anatase, rutile and brookite TiO. Iron oxide nanocatalyst with titanium and silver nanoparticles: Synthesis, characterization and photocatalytic activity on the degradation of Rhodamine B dye. (c) Proposed mechanism for degradation of PP/TiO2-OMT composite [68]; reprinted from [68] with permission from John Wiley and Sons. Please note that many of the page functionalities won't work as expected without javascript enabled. Therefore, engineering plastic degradation processes such as photodegradation [6,8], thermo-oxidative degradation [9,10], and biodegradation [11] have attracted intensive research interest. Moreover, the photocatalytic activity of PE-TiO2 can be improved using modified TiO2 photocatalysts such as multiwalled carbon nanotube (MWCNT)-TiO2 composite (TiO2-MWCNTs) [75], polypyrrole(PPy)-TiO2 composite (PPy/TiO2) [76], and polyacrylamide grafted TiO2 (PAM-g-TiO2) [77]. Energy band structure (left panel) and DOS (right panel) for (a) anatase and (b) rutile TiO2 [27]; reproduced from [27] with permission from the PCCP Owner Societies. Micromachines. Moreover, it is regarded that the interfacial charge transfer at the surface of the semiconductor is important in producing hydroxyl radicals, affecting the overall photocatalytic degradation rate [33]. Spectrochim. As expected, the degradation efficiency is always relatively higher for the latter. Lastly, in the termination step [8], the free radicals produced react with each other to undergo the crosslinking reaction for the formation of inert products (Path 9). Photodegradation of PE. official website and that any information you provide is encrypted In the initiation step, the existence of chromophore group, which absorbs the incident light due to energy matching, in the polymers structure is important to act as the photo-initiator [8]. The resin identification code (RIC) system created by the Society of Plastic Industry (SPI) is often used to categorize the type of plastic during production and to facilitate post-consumer plastic recycling. Eff. Mater. The lower the position of VBM of a semiconductor, the higher the oxidation capability it has. In addition, the hydroperoxides react with another hydroperoxide to form polymer alkoxy radicals, polymer peroxide radicals, and water (Path 5).
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