Photocatalytic oxidation technology for indoor air pollutants elimination: A review

Facile synthesis of activated carbon/titanium dioxide composite and its application for adsorptive/photocatalytic removal of gaseous toluene

This study explores the practical utility of activated carbon/titanium dioxide (AC/TiO2) composite for the abatement of a common aromatic volatile organic compound (VOC), toluene. The performance of the prepared AC/TiO2 composite (ACT-x: x as the theoretical mass ratio (in percent) of AC over TiO2 ranging from 0% to 10%) is evaluated individually as an adsorbent and photo-catalyst against gaseous toluene in a packed flow tube reactor under varying operational conditions (e.g., relative humidity and gaseous pollutant composition). The incorporation of AC into TiO2 significantly increases its adsorption capacity (Q), e.g., 1.71 mg g-1 for ACT-10 (relative to 0.01 mg g-1 for ACT-0). The ACT-5, with 3.6% C, exhibits the maximum photocatalytic removal efficiency (XT = 93.77%), quantum efficiency (QE; 1.63 × 10-4 molecules photon-1), space time yield (STY; 1.99 × 10-5 molecules photon-1 mg-1), and specific clear air delivery rate (SCADR; 686.2 L h-1 g-1) of the compositions tested. ACT composite exhibits enhanced adsorption and in-situ degradation-desorption process to facilitate the capture of VOCs while diminishing the generation of by-products. The in-situ diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry analyses indicate the formation of several intermediate by-products during the photocatalytic degradation process, including benzyl alcohol, benzaldehyde, benzoic acid, phenol, and alkane species, through ring-opening reactions. In addition, the photocatalytic performance of ACT is demonstrated to be superior to those of other TiO2-based photocatalysts. Accordingly, the ACT composite is recommended as a promising medium for the abatement of aromatic VOCs in indoor air.

Study on the Effectiveness of a Copper Electrostatic Filtration System "Aerok 1.0" for Air Disinfection

BACKGROUND

Bioaerosols can represent a danger to health. During SARS-CoV-2 pandemic, portable devices were used in different environments and considered a valuable prevention tool. This study has evaluated the effectiveness of the air treatment device "AEROK 1.0®" in reducing microbial, particulate, and pollen airborne contamination indoors, during normal activity.

METHODS

In an administrative room, airborne microbial contamination was measured using active (DUOSAS 360 and MD8) and passive sampling; a particle counter was used to evaluate particle concentrations; a Hirst-type pollen trap was used to assess airborne pollen and Alternaria spores. Statistical analysis was performed using SPSS 26.0; p values < 0.05 were considered statistically significant.

RESULTS

The airborne bacterial contamination assessed by the two different samplers decreased by 56% and 69%, respectively. The airborne bacterial contamination assessed by passive sampling decreased by 44%. For fungi, the reduction was 39% by active sampling. Airborne particles (diameters ≥ 1.0, 2.0 μm) and the ratio of indoor/outdoor concentrations of total pollen and Alternaria spp. spores significantly decreased.

CONCLUSIONS

The results highlight the effectiveness of AEROK 1.0® in reducing airborne contamination. The approach carried out represents a contribution to the definition of a standardized model for evaluating the effectiveness of devices to be used for air disinfection.

Synergistic mechanisms of carbon-based materials for VOCs photocatalytic degradation: A critical review

With the rapid expansion of human activities, there has been a significant increase in the release of volatile organic compounds (VOCs) from factories and interior decoration materials, posing a substantial risk to the surrounding ecosystem and human health. Photocatalysis technology based on semiconductors has emerged as a promising solution for mitigating atmospheric pollution and indoor air quality concerns. However, single semiconductors encounter several challenges when it comes to VOC photodegradation, including issues like the weak adsorption capacity for VOC molecules, insufficient surface-active sites, and limited light utilization. In recent decades, carbon-based materials have gained considerable interest in photodegrading VOCs owing to their strong adsorption capacity, electrical conductivity, broad light absorption range, and tunable surface characteristics. The incorporation of carbon materials can enhance the photodegradation efficiency of VOCs by facilitating the transfer of VOCs from the ambient air to the surface of the photocatalysts, increasing the number of active surface sites, expanding the light absorption region, and promoting the separation of charge carriers. This review provides a comprehensive overview of the applications of carbon materials with different dimensions in enhancing the performance of semiconductors for the photocatalytic degradation of VOCs. Based on the fundamental principles of photocatalytic VOC degradation, this review explores the factors influencing the degradation performance of catalysts and elucidates the degradation mechanisms. Moreover, it summarizes a range of synthesis approaches for carbon-based photocatalysts, discussing the multiple roles played by carbon materials in these processes. In conclusion, the review offers insights into the current state of carbon-based photocatalysts and outlines the existing challenges. It also provides a perspective on the future development of these materials, highlighting the need for continued research and innovation in this field.

Facile Light-Driven Synthesis of Highly Luminous Sulfur Quantum Dots for Fluorescence Sensing and Cell Imaging

Sulfur quantum dots (SQDs) are emerging fluorescent nanomaterials, whereas most of the methods for synthesizing SQDs are limited to thermal synthesis. In this study, we report the first case of a light-driven strategy for facile synthesis of SQDs and further applied the SQDs for fluorescence cell imaging. The light-driven synthesis strategy only utilized Na2S as the sulfur source and nano-TiO2 as the photosensitizer. Under ultraviolet illumination, the nano-TiO2 photosensitizer generated a large number of •O2- and •OH to oxidize S2- to Sx2- and further to elemental sulfur, which could be obtained as monodispersed SQDs after etching by H2O2. The prepared SQDs exhibit excellent tunable photoluminescence properties, superior stability, and a uniform small size, with particle diameters in the range of 0.5-4 nm, and the fluorescence absolute quantum yield is as high as 27.8%. Meanwhile, the prepared SQDs also exhibited extreme biocompatibility and stability, and we further applied it for intracellular imaging and Hg2+ sensing with satisfactory results. In comparison to the widely reported thermal synthesis, the light-driven synthesis method is greener and simpler, opening a new way for the preparation of biocompatible SQDs.

Separation processes for the treatment of industrial flue gases - Effective methods for global industrial air pollution control

The treatment of flue gases has become a crucial area of interest with the increasing air emissions into the atmosphere from industries involved in combustion of fossil fuels in their operations. In essence, there is a critical need for effective methods of treatment more than ever. Treatment and separation are now a demand for the overall industrial operations to control the rate of flue gas emissions. The major culprit in this wise is power generating industry. The major associated air pollutants are carbon dioxide, sulfur oxides, trace metals, volatile organic compounds, particulate matters, and nitrogen oxides. However, the choice of technologies to be utilized requires more than just knowledge of the separation process, but also a good understanding of the properties of the pollutants. This review explored and evaluated the various separation processes and technologies for the treatment of industrial flue gases for the control of the associated air pollutants. It also analyzed the performance with references to cost and efficiency, the advantages and disadvantages, principles for selection, research direction, and/or potential opportunities in existing separation processes and technologies.

Neural network-based performance assessment of one- and two-liquid phase biotrickling filters for the removal of a waste-gas mixture containing methanol, α-pinene, and hydrogen sulfide

The performance of one- and two-liquid phase biotrickling filters (OLP/TLP-BTFs) treating a mixture of gas-phase methanol (M), α-pinene (P), and hydrogen sulfide (H) was assessed using artificial neural network (ANN) modeling. The best ANN models with the topologies 3-9-3 and 3-10-3 demonstrated an exceptional capacity for predicting the performance of O/TLP-BTFs, with R2 > 99%. The analysis of causal index (CI) values for the model of OLP-BTF revealed a negative impact of M on P removal (CI = -2.367), a positive influence of P and H on M removal (CI = +7.536 and CI = +3.931) and a negative effect of H on P removal (CI = -1.640). The addition of silicone oil in TLP-BTF reduced the negative impact of M and H on P degradation (CI = -1.261 and CI = -1.310, respectively) compared to the OLP-BTF. These findings suggested that silicone oil had the potential to improve P availability to the biofilm by increasing the concentration gradient of P between the air/gas and aqueous phases. Multi-objective particle swarm optimization (MOPSO) suggested an optimum operational condition, i.e. inlet M, P, and H concentrations of 1.0, 1.1, and 0.3 g m-3, respectively, with elimination capacities (ECs) of 172.1, 26.5, and 0.025 g m-3 h-1 for OLP-BTF. Likewise, one of the optimum operational conditions for TLP-BTF is achievable at inlet concentrations of 4.9, 1.7, and 0.8 g m-3, leading to the optimum ECs of 299.7, 52.9, and 0.072 g m-3 h-1 for M, P, and H, respectively. These results provide important insights into the treatment of complex waste gas mixtures, addressing the interactions between the pollutant removal characteristics in OLP/TLP-BTFs and providing novel approaches in the field of biological waste gas treatment.

Efficient deactivation of aerosolized pathogens using a dielectric barrier discharge based cold-plasma detergent in environment device for good indoor air quality

Air pollution is one of the top 5 risks causing chronic diseases according to WHO and airborne transmitted pathogens infection is a huge challenge in the current era. Long living pathogens and small size aerosols are not effectively dealt with by the available indoor air purifiers. In this work, a dielectric barrier discharge (DBD) based portable cold-plasma detergent in environment device is reported and its disinfection efficiency has been analyzed in the indoor environment of sizes up to 3 × 2.4 × 2.4 m³. The deactivation efficiency of total microbial counts (TMCs) and total fungal counts (TFCs) is found to be more than 99% in 90 min of continuous operation of the device at the optimized parameters. The complete inactivation of MS2 phage and Escherichia coli bacteria with more than 5 log reduction (99.999%) has also been achieved in 30 min and 90 min of operation of the device in an enclosed environment. The device is able to produce negative ions predominantly dominated by natural plasma detergent along with positive ions in the environment similar to mother nature. The device comprises a coaxial DBD geometry plasma source with a specially designed wire mesh electrode of mild steel with a thickness of 1 mm. The need for feed gas, pellets and/or differential pressure has been eliminated from the DBD discharge source for efficient air purification. The existence of negative ions for more than 25 s on average is the key advantage, which can also deactivate long living pathogens and small size aerosols.

Preparation of dual-use GPTES@ZnO photocatalyst from waste warm filter cake and evaluation of its synergic photocatalytic degradation for air-water purification

Organic pollutants are the most critical threats to the health of air and water resources. On this basis, fabricating a photocatalytic acrylic film with dual-use (i.e. removing benzene from air and MB/MO dyes from water) was aimed in this research. For this purpose, waste warm filter cake (WWFC) was used to extract zinc from it. Zinc element was separated from WWFC by a basic leaching method and acidified to prepare zinc oxide nanoparticles. In the following, a simple hydrothermal method was used to increase the surface functionality of the extracted ZnO nanoparticles in order to establish active reaction sites for reaction to silane coupling agent and increase in the holes that were prepared during photo-excitation. Thereafter, the nanoparticles were modified with 3-glycidoxypropyltriethoxysilane (GPTES) at different concentrations. The band gap of the modified nanoparticles decreased from 3.25 to 3.1 eV by surface modification. The photocatalytic performance of ZnO nanoparticles was assessed by degradation of MB and MO aqueous solution (50 ppm) under simulated UV/Visible irradiations. MB and MO were degraded 91 and 60% under UV light and 65 and 50% under visible light after 150 min of irradiation. The photo degradation rate increased after adding carboxy methyl cellulose (CMC) surfactant to methylene blue and adding cocamide-dea (CDE-G) surfactant to methyl orange. The results confirmed that the green surfactants improve the dispersion and surface interaction of the modified nanoparticles in the dyes solution and cause more electron charge transfer which creates effective photocatalytic sites. The prepared nanocomposite films were placed in a photo-reactor to remove gaseous benzene from air under UV/visible irradiation. Gas chromatography (GC) results showed that the modified nanoparticles removed up to 35.25 and 20.34% of benzene from air. Colorimetric analysis (ΔE*) showed that the acrylic film contained modified nanoparticles degraded 91 and 82% of MB, and 85 and 76% of MO under UV/visible lights, respectively. In the end, it can be said that these photocatalytic films are able to remove environmental pollution in air and water.

TiO2-based catalytic systems for the treatment of airborne aromatic hydrocarbons

Among diverse strategies to manage air quality, catalytic oxidation has been a widely used option to mitigate diverse pollutants such as aromatic volatile organic compounds (VOCs), especially benzene, toluene, and xylene (BTX). For such applications, TiO₂-based catalysts have drawn significant research attention for their prominent photo/thermal catalytic activities and photochemical stability. This review has been organized to elaborate on the recent developments achieved in the thermocatalytic, photocatalytic, and photothermal applications of metal/non-metal doped TiO₂ catalysts towards BTX vapors and their reaction mechanisms. The performance of the reported TiO₂-based catalysts has also been analyzed based on multiple computational metrics such as reaction rate (r), quantum yield (QY), space-time yield, and figure of merit (FOM). At last, the research gap and prospects in the catalytic treatment of BTX are also discussed in association with the feasibility and utility of TiO₂-based catalysts in air purification applications.

Revelation of contributing mechanism of reactive oxygen species in photocatalytic ozonation heterocyclization of gaseous hexane isomers

The reactive oxygen species (ROS) involved photocatalytic ozonation of gaseous n-hexane to heterocyclic compounds has been recently reported. However, whether such heterocyclization reaction happens on other alkanes and what is the contributing mechanism of ROS to the heterocyclic compound formation are still unclear. In present study, photocatalytic ozonation of three n-hexane's isomers (i.e. 2-methypentane, 3-methylpentane and 2,3-dimethylbutane) on Cu₂O-CuO/TiO₂-foam ceramic was investigated. Within reaction period, 2-methylpentane and 3-methylpentane not only showed higher average degradation efficiency than 2,3-dimethylbutane, but also separately converted to interfacial heterocyclic compounds of 5,5-dimethyldihydro-2(3H)-furanone and 4,5-dimethyl-4,5-dihydro-2(3H)-furanone. Enough reaction time, optimum experimental atmosphere and shorter light wavelength benefited the formation of heterocyclization products. None of O₃, ¹O₂, electron and hole directly contributed to the heterocyclic compound formation. While ^•O₂^- dominated the production of the heterocyclic compound under the dry reaction atmosphere and ^•OH showed more important role than ^•O₂^- in the heterocyclic compound formation under the moist reaction atmosphere. Theoretical calculation confirmed that ^•OH or ^•O₂^- induced heterocyclization reaction of alkane was exothermic, while the former reaction released 0.47 eV higher energy than the later reaction. The findings provide a comprehensive understanding of contributing roles of ROS in heterocyclization reaction of alkanes, and are helpful for effective elimination of industrial alkanes by advanced oxidation methods.

Recent Developments in Photocatalytic Nanotechnology for Purifying Air Polluted with Volatile Organic Compounds: Effect of Operating Parameters and Catalyst Deactivation

Photocatalytic oxidation (PCO) is a successful method for indoor air purification, especially for removing low-concentration pollutants. Volatile organic compounds (VOCs) form a class of organic pollutants that are released into the atmosphere by consumer goods or via human activities. Once they enter the atmosphere, some might combine with other gases to create new air pollutants, which can have a detrimental effect on the health of living beings. This review focuses on current developments in the degradation of indoor pollutants, with an emphasis on two aspects of PCO: (i) influence of environmental (external) conditions; and (ii) catalyst deactivation and possible solutions. TiO2 is widely used as a photocatalyst in PCO because of its unique properties. Here, the potential effects of the operating parameters, such as the nature of the reactant, catalyst support, light intensity, and relative humidity, are extensively investigated. Then the developments and limitations of the PCO technique are highlighted, especially photocatalyst deactivation. Furthermore, the nature and deactivation mechanisms of photocatalysts are discussed, with possible solutions for reducing catalyst deactivation. Finally, the challenges and future directions of PCO technology for the elimination of indoor pollutants are compared and summarized.

Solar-induced efficient propylparaben photodegradation by nitrogen vacancy engineered reticulate g-C3N4: Morphology, activity and mechanism

Propylparaben (PrP) has attracted extensive concerns due to its wide occurrence in wastewater and potential health risk. Herein, nitrogen vacancy engineered reticulate g-C₃N₄ (Nv-RCN) was successfully synthesized for the photodegradation of PrP. Nv-RCN exhibited larger specific surface area, greater light absorption ability, higher transfer and separation efficiency of charge carriers in comparison with bulk g-C₃N₄ (CN). According to the characterization results and DFT calculation, nitrogen vacancy could capture electrons and facilitate oxygen adsorption. The Nv-RCN exhibited an outstanding PrP removal efficiency of 94.3 %, and the corresponding apparent rate constant of Nv-RCN was 3.37 times higher than that of CN. High O₂ concentration (8 mg/L) and low pH value (pH = 3) promoted PrP photodegradation based on Box-Behnken Design. The O₂^- was the major radical during PCOP of Nv-RCN, and could oxidize PrP by decarbonylation and dealkylation. This study provided new insights to the improvement of photodegradation performance of g-C₃N₄ for parabens removal and related environmental remediation.

Recent progress on electrospun nanofibrous polymer membranes for water and air purification: A review

Developing new polymer membranes with excellent thermal, mechanical, and chemical stability has shown great potential for various environmental remediation applications such as wastewater treatment and air filtration. Polymer membranes have been widely investigated over the past years and utilized to overcome severe ecological issues. Membrane-based technologies play a critical role in water purification and air filtration with the ability to act efficiently and sustainably. Electrospun nanofiber membranes have displayed excellent performance in removing various contaminants from water, such as bacteria, dyes, heavy metals, and oil. These nanofibrous membranes have shown good potential to filter the air from tiny particles, volatile organic compounds, and toxic gases. The performance of polymer membranes can be enhanced by fine-tuning polymer structure, varying surface properties, and strengthening overall membrane porosity. In this review, we discuss the involvement of electrospun nanofibrous membranes in different environmental remediation applications. It further reviews the recent progress of polymer membrane development by utilizing nanoparticles and naturally occurring polymers.

Novel monolithic catalysts for VOCs removal: A review on preparation, carrier and energy supply

Volatile organic compounds (VOCs) are considered the culprit of secondary air pollution such as ozone, secondary organic aerosols, and photochemical smog. Among various technologies, catalytic oxidation is considered a promising method for the post-treatment of VOCs. Researchers are sparing no effort to develop novel catalysts to meet the requirements of the catalytic process. Compared with the powdered or granular catalysts, the monolithic catalysts have the advantages of low pressure drop, high utilization of active phases, and excellent mechanical properties. This review summarized the new design of monolithic catalysts (including new preparation methods, new supports, and new energy supply methods) for the post-treatment of VOCs. It addressed the advantages of the new designs in detail, and the scope of applicability for each new monolithic catalyst was also highlighted. Finally, the highly required future development trends of monolithic catalysts for VOCs catalytic oxidation are recommended. We expect this work can inspire and guide researchers from both academic and industrial communities, and help pave the way for breakthroughs in fundamental research and industrial applications in this field.

Recent advancement in conjugated polymers based photocatalytic technology for air pollutants abatement: Cases of CO2, NOx, and VOCs

According to World Health Organization (WHO) survey, air pollution has become the major reason of several fatal diseases, which had led to the death of 7 million peoples around the globe. The 9 people out of 10 breathe air, which exceeds WHO recommendations. Several strategies are in practice to reduce the emission of pollutants into the air, and also strict industrial, scientific, and health recommendations to use sustainable green technologies to reduce the emission of contaminants into the air. Photocatalysis technology recently has been raised as a green technology to be in practice towards the removal of air pollutants. The scientific community has passed a long pathway to develop such technology from the material, and reactor points of view. Many classes of photoactive materials have been suggested to achieve such a target. In this context, the contribution of conjugated polymers (CPs), and their modification with some common inorganic semiconductors as novel photocatalysts, has never been addressed in literature till now for said application, and is critically evaluated in this review. As we know that CPs have unique characteristics compared to inorganic semiconductors, because of their conductivity, excellent light response, good sorption ability, better redox charge generation, and separation along with a delocalized π-electrons system. The advances in photocatalytic removal/reduction of three primary air-polluting compounds such as CO₂, NO_X, and VOCs using CPs based photocatalysts are discussed in detail. Furthermore, the synergetic effects, obtained in CPs after combining with inorganic semiconductors are also comprehensively summarized in this review. However, such a combined system, on to better charges generation and separation, may make the Adsorb & Shuttle process into action, wherein, CPs may play the sorbing area. And, we hope that, the critical discussion on the further enhancement of photoactivity and future recommendations will open the doors for up-to-date technology transfer in modern research.

An overview on recent progress in photocatalytic air purification: Metal-based and metal-free photocatalysis

Air pollution is becoming a distinctly growing concern and the most pressing universal problem as a result of increased energy consumption, with the multiplication of the human population and industrial enterprises, resulting in the generation of hazardous pollutants. Among these, carbon monoxide, nitrogen oxides, Volatile organic compounds, Semi volatile organic compounds, and other inorganic gases not only have an adverse impact on human health both outdoors and indoors, but have also substantially altered the global climate, resulting in several calamities around the world. Thus, the purification of air is a crucial matter to deal with. Photocatalytic oxidation is one of the most recent and promising technologies, and it has been the subject of numerous studies over the past two decades. Hence, the photocatalyst is the most reassuring aspirant due to its adequate bandgap and exquisite stability. The process of photocatalysis has provided many benefits to the atmosphere by removing pollutants. In this review, our work focuses on four main themes. Firstly, we briefly elaborated on the general mechanism of air pollutant degradation, followed by an overview of the typical TiO₂ photocatalyst, which is the most researched photocatalyst for photocatalytic destruction of gaseous VOCs. The influence of operating parameters influencing the process of photocatalytic oxidation (such as mass transfer, light source and intensity, pollutant concentration, and relative humidity) was then summarized. Afterwards, the progress and drawbacks of some typical photoreactors (including monolithic reactors, microreactors, optical fiber reactors, and packed bed reactors) were described and differentiated. Lastly, the most noteworthy coverage is dedicated to different types of modification strategies aimed at ameliorating the performance of photocatalysts for degradation of air pollutants, which were proposed and addressed. In addition, the review winds up with a brief deliberation for more exploration into air purification photocatalysis.

Mn2+ doped AgInS2 photocatalyst for formaldehyde degradation and hydrogen production from water splitting by carbon tube enhancement

In this work, AgInS₂ and Mn²⁺ doped AgInS₂ (Mn-AgInS₂) with different Mn²⁺: (Ag⁺ + In³⁺) ratios were synthesized via a low temperature liquid method. The photocatalytic activity of the obtained samples was followed by taking formaldehyde as the target pollutant under visible light irradiation. The photocatalysts were passed through various characterization procedures to investigate their morphological, structural and photophysical characteristics. The optimal proportion sample [with the ratio n (Mn²⁺): n (Ag⁺ + In³⁺) = 1:100] photodegraded about 79% formaldehyde in 150 min. These upgraded activities are attributed to the enhanced visible light absorption and superior charge separation due to the presence of Mn²⁺ as confirmed site from charge separation measurements. In addition, a possible mechanism for the photodegradation of formaldehyde is proposed based on the experimental results. Furthermore, the photocatalytic water splitting performance of Mn-AgInS₂ and multi-walled carbon nanotubes (MWCNTs) modified Mn-AgInS₂ is investigated and compared under simulated sunlight irradiation, and remarkable hydrogen production is achieved (105 μmol h^-1 g^-1) by using the latter.

Recent Advances in Vehicle Exhaust Treatment with Photocatalytic Technology

Vehicle exhaust has been acknowledged as an essential factor affecting human health due to the extensive use of cars. Its main components include volatile organic compounds (VOCs) and nitrogen oxides (NOx), which can cause acute irritation and chronic diseases, and significant research on the treatment of vehicle exhaust has received increasing attention in recent decades. Recently, photocatalytic technology has been considered a practical approach for eliminating vehicle emissions. This review highlights the crucial role of photocatalytic technology in eliminating vehicle emissions using semiconductor catalysts. A particular emphasis has been placed on various photocatalytic materials, such as TiO2-based materials, Bi-based materials, and Metal–Organic Frameworks (MOFs), and their recent advances in the performance of VOC and NOx photodegradation. In addition, the applications of photocatalytic technology for the elimination of vehicle exhaust are presented (including photocatalysts combined with pavement surfaces, making photocatalysts into architectural coatings and photoreactors), which will offer a promising strategy for photocatalytic technology to remove vehicle exhaust.

Synergetic effect of photocatalysis and peroxymonosulfate activated by MFe2O4 (M = Co, Mn, or Zn) for enhanced photocatalytic activity under visible light irradiation

Nanosized MFe2O4 (M = Co, Mn, or Zn) photocatalysts were synthesized via a simple sol-gel method. MFe2O4 photocatalysts exhibited lower photocatalytic activity for the degradation of levofloxacin hydrochloride under visible light irradiation. For enhancement of photocatalytic activity, MFe2O4 was used to activate peroxymonosulfate and degrade levofloxacin hydrochloride under visible light irradiation. The influences of peroxymonosulfate dosage, levofloxacin hydrochloride concentration, pH value, and temperature on peroxymonosulfate activation to degrade levofloxacin hydrochloride were investigated in detail. The mechanism of activation of peroxymonosulfate by MFe2O4 was proposed and proved by radical quenching experiments, electron spin resonance analysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and transient photocurrent responses. The combined activation effects of photogenerated e-/h+ and transition metals on peroxymonosulfate to produce sulfate radical clearly enhanced the degradation efficiency.

Nano Metal-Containing Photocatalysts for the Removal of Volatile Organic Compounds: Doping, Performance, and Mechanisms

Volatile organic compounds (VOCs) in indoor air are considered a major threat to human health and environmental safety. The development of applicable technologies for the removal of VOCs is urgently needed. Nowadays, photocatalytic oxidation (PCO) based on metal-containing photocatalysts has been regarded as a promising method. However, unmodified photocatalysts are generally limited in applications because of the narrow light response range and high recombination rate of photo-generated carriers. As a result, nano metal-containing photocatalysts doped with elements or other materials have attracted much attention from researchers and has developed over the past few decades. In addition, different doping types cause different levels of catalyst performance, and the mechanism for performance improving is also different. However, there are few reviews focusing on this aspect, which is really important for catalyst design and application. This work aims to give a comprehensive overview of nano metal-containing photocatalysts with different doping types for the removal of VOCs in an indoor environment. First, the undoped photocatalysts and the basic mechanism of PCO is introduced. Then, the application of metal doping, non-metal doping, co-doping, and other material doping in synthetic metal-containing photocatalysts are discussed and compared, respectively, and the synthesis methods, removal efficiency, and mechanisms are further investigated. Finally, a development trend for using nano metal-containing photocatalysts for the removal of VOCs in the future is proposed. This work provides a meaningful reference for selecting effective strategies to develop novel photocatalysts for the removal of VOCs in the future.

Postharvest Ultraviolet Radiation in Fruit and Vegetables: Applications and Factors Modulating Its Efficacy on Bioactive Compounds and Microbial Growth

Ultraviolet (UV) radiation has been considered a deleterious agent that living organisms must avoid. However, many of the acclimation changes elicited by UV induce a wide range of positive effects in plant physiology through the elicitation of secondary antioxidant metabolites and natural defenses. Therefore, this fact has changed the original UV conception as a germicide and potentially damaging agent, leading to the concept that it is worthy of application in harvested commodities to take advantage of its beneficial responses. Four decades have already passed since postharvest UV radiation applications began to be studied. During this time, UV treatments have been successfully evaluated for different purposes, including the selection of raw materials, the control of postharvest diseases and human pathogens, the elicitation of nutraceutical compounds, the modulation of ripening and senescence, and the induction of cross-stress tolerance. Besides the microbicide use of UV radiation, the effect that has received most attention is the elicitation of bioactive compounds as a defense mechanism. UV treatments have been shown to induce the accumulation of phytochemicals, including ascorbic acid, carotenoids, glucosinolates, and, more frequently, phenolic compounds. The nature and extent of this elicitation have been reported to depend on several factors, including the product type, maturity, cultivar, UV spectral region, dose, intensity, and radiation exposure pattern. Even though in recent years we have greatly increased our understanding of UV technology, some major issues still need to be addressed. These include defining the operational conditions to maximize UV radiation efficacy, reducing treatment times, and ensuring even radiation exposure, especially under realistic processing conditions. This will make UV treatments move beyond their status as an emerging technology and boost their adoption by industry.

Current progress on catalytic oxidation of toluene: a review

Toluene is one of the pollutants that are dangerous to the environment and human health and has been sorted into priority pollutants; hence, the control of its emission is necessary. Due to severe problems caused by toluene, different techniques for the abatement of toluene have been developed. Catalytic oxidation is one of the promising methods and effective technologies for toluene degradation as it oxidizes it to CO₂ and does not deliver other pollutants to the environment. This paper highlights the recent progressive advancement of the catalysts for toluene oxidation. Five categories of catalysts, including noble metal catalysts, transition metal catalysts, perovskite catalysts, metal-organic frameworks (MOFs)-based catalysts, and spinel catalysts reported in the past half a decade (2015-2020), are reviewed. Various factors that influence their catalytic activities, such as morphology and structure, preparation methods, specific surface area, relative humidity, and coke formation, are discussed. Furthermore, the reaction mechanisms and kinetics for catalytic oxidation of toluene are also discussed.