Photocatalytic Oxidation Process Research Articles

Economics of enhanced methane oxidation relative to carbon dioxide removal

Mitigating short-term global warming is imperative, and a key strategy involves reducing atmospheric methane (CH4) due to its high radiative forcing and short lifespan. This objective can be achieved through methods such as oxidising methane at its source or implementing enhanced oxidation techniques to reduce atmospheric CH4 concentrations. In this study, we use a range of metrics to analyse both the impact and value of enhanced CH4 oxidation relative to carbon dioxide (CO2) removal on global temperature. We apply these metrics to a select group of model studies of thermal-catalytic, photocatalytic, biological and capture-based oxidation processes under different greenhouse gas (GHG) concentrations. Using a target cost of €220-1000/tCO2 for CO2 removal, our findings indicate that metrics valuing enhanced oxidation techniques based on their contribution to mitigating the long-term level of warming show these techniques are uncompetitive with CO2 removal. However, when using metrics that value enhanced oxidation of CH4 based on its impact on the immediate rate of warming, photocatalytic methods may be competitive with CO2 removal, whereas biofiltration, thermal-catalytic oxidation and capture-based units remain uncompetitive. We conclude that if the policy goal is to target the immediate rate of warming, it may be more valuable to incentivise CO2 removal and enhanced oxidation of methane under separate GHG targets.

Semiconductor Catalyst: Investigation for the Degradation of BB9 Azo Dye by Sonophotocatalytic Process

AbstractThe degradability of an azo dye, Basic Blue 9 (BB9), by heterogeneous sonocatalytic, photocatalytic, and sonophotocatalytic oxidation process was examined using simultaneous irradiation of UV‐C at 254 nm and power ultrasound at 20 kHz accompanied with a heterogeneous catalyst zinc oxide (ZnO) in the study. The effect of ZnO dose and initial dye concentration was investigated on the dye degradation in sonocatalytic, photocatalytic, and sonophotocatalytic processes at pH 5.5 (natural pH). The results obtained from the experimental studies were evaluated with the parameters of color removal, pseudo‐first‐order rate constant, and half‐life time. It was observed that the degradation of BB9 dye by the sonophotocatalytic process was higher compared to both sonocatalytic and photocatalytic degradation. as follows: 97.46, 48.64 and 56.88 %. The combination of sono and photocatalytic showed a remarkable synergistic effect in BB9 degradation. The kinetics of sonophotocatalytic oxidations, depending on the initial BB9 dye concentration, were found to follow the Langmuir‐Hinshelwood model. In addition, the effect of ZnO on the sonophotocatalytic oxidation process was higher compared to titanium dioxide and zero‐valent iron as follows: 97.47, 80.77 and 80.62 %.

Cyclodextrin-boosted photocatalytic oxidation for efficient bisphenol A removal

Wastewater contains various high-risk trace organic pollutants, such as antibiotics and endocrine disruptors, which seriously restrict wastewater reuse. Cyclodextrin-based functional materials show great potential in the removal of trace pollutants because of their adsorption catalytic synergy. Clarifying the synergistic mechanism of cyclodextrin in oxidation is the key issue in confined catalytic oxidation process design. In this work, we fabricated a BiOIO3@BiOBr/β-CD heterojunction photocatalyst to study the synergistic mechanism of cyclodextrin in the photocatalytic oxidation process. The synergistic mechanism of cyclodextrin was investigated by combining radical chemistry, electrochemistry, spectroscopy, and time-dependent density functional theory. Results showed that the excited intermediate free radicals played an important role in promoting the photocatalytic degradation process. The heterojunction photocatalyst loaded with β-cyclodextrin (β-CD) at the electronic end (C[Cat.] = 0.2 mg/mL) removed about 97% of bisphenol A (BPA) within 30 min, and the first-order kinetic constant (kCDBIB = 0.112 min−1) was about twice that of the unloaded β-CD (kBIB = 0.057 min−1). Cyclodextrin loading improved the photocatalytic performance of the heterojunction and stimulated the intermediate to increase the free radical yield and regulate the reaction path.

Development of Fe/HNT and Fe/HNT-Al2O3 composite catalysts and application in successive treatment processes for pharmaceutical industry wastewater

The pharmaceutical industry wastewater (PIW) was treated by successive use of electro Fenton (EF) and photocatalytic oxidation (PcO) processes. Nano-particular powdered Fe/HNT (Iron/Halloysite nanotube) heterogeneous semiconductor catalyst was initially produced with Fe(OH)3 sludge modification precipitated after EF process. Thus, photocatalyst material was produced from the waste sludge and used in the PcO process. Photocatalyst Fe/HNT powder was immobilized on a three-dimensional (3D) reticulated Al2O3 ceramic support to enable rapid recovery of the catalyst from the PcO reactor system. Particle morphology and chemical configuration of the heterogeneous catalysts were analyzed with SEM (Scanning Electron Microscopy)-EDS (Energy-Dispersive X-ray spectrometry), UV-DRS (Ultraviolet Diffuse Reflectance Spectra) and XRD (X-ray diffraction). The Fe/HNT layer was calcined at three different temperatures (350, 450 and 600 °C). The optimum temperature was determined as 350 °C for better photocatalytic performance and practical reasons such as energy consumption. The successive use of EF + PcO processes for degradation of three different PIW samples was investigated by using two catalyst forms (nanoparticle and reticulated) and light sources (visible and sun light). The max TOC removal efficiency by EF + sun light-PcO (with Fe/HNT) successive treatment process was obtained as 78.4 %. Besides, the energy consumption value was calculated for optimum process state and calculated as 48.8 kWh/kg TOC at the EF + sun light-PcO (with Fe/HNT) successive treatment process.

Engineering bifunctional sites in covalent polymers for boosting photocatalytic H2S oxidation

The development of catalyst for photocatalytic hydrogen sulfide (H2S) oxidation with excellent efficiency and regeneration properties is a significant challenge. Herein, the pyridine units as bifunctional sites are incorporated in covalent polymers (CPs) by CN coupling reaction, which exhibit photocatalytic H2S selective oxidation to sulfur conversion (95 %) under visible light in a continuous flow system, more than twice that of the pristine sample (40 %). Meanwhile, the photocatalytic H2S conversion rate had a linear function relationship with pyridinic N content, demonstrating the substantial role of pyridine in photocatalytic H2S oxidation process. According to experimental results, the pyridine unit not only acted as the structural base site to improve the H2S chemisorption, but also served as electron withdrawing unit to construct electron donor-acceptor (D-A) structure with benzene, which optimized the light absorption, charge separation and migration. In addition, series in-situ measurements and electron density difference simulations revealed the significant role of electron D-A structure in H2S adsorption and activation process. By exploring the effect of pyridine unit in CPs on H2S conversion process, this work provides a new idea for the subsequent study of photocatalytic H2S oxidation.

Solvothermal synthesis of Bi12TiO20/Bi4Ti3O12 heterostructure with highly efficient photodegradation of MO under UV irradiation

The sillenite-structured bismuth titanate (Bi12TiO20) is thought to be a viable photocatalyst for environmental remediation. However, the performance of Bi12TiO20 as a photocatalyst is severely constrained by its limited range of light sensitivity and the rapid photoinduced electron-hole pair recombination. A practical and effective way to overcome these limitations is to combine Bi12TiO20 with adequate photocatalysts to create heterojunctions. Here, a one-step solvothermal technique is used to synthesize Bi12TiO20/Bi4Ti3O12 heterojunction (BTO). The electric field that exists between B12TiO20, Bi4Ti3O12 and the closed interfacial contacts had a synergistic effect on the constructed composites, which resulted in high charge transfer abilities. Therefore, the BTO heterojunction demonstrated increased photocatalytic efficacy in the presence of ultraviolet irradiation. The MO removal efficiency of optimal BTO was 97.15%, significantly higher than that of pure Bi2O3 (46.9%). Furthermore, the cycling experiment demonstrated that the BTO heterojunction is stable and reusable. The probable mechanism of photocatalytic MO oxidation over BTO heterojunction was studied by various scavengers. The •OH radicals and holes played essential roles in BTO system of photocatalytic oxidation process.

Low concentration of peroxymonosulfate coupled with visible light triggers oxygen reactive species generation over constructed Bi25FeO40/BiOCl Z-scheme heterojunction for various tetracycline antibiotics removal

Photocatalytic peroxymonosulfate (PMS) oxidation systems demonstrate significant potential and promising prospects through the interconnection of photocatalytic and PMS oxidation for simultaneously achieving efficient pollutant removal and reduction of PMS dosage, which prevents resource wastage and secondary pollution. In this study, a Z-scheme Bi25FeO40/BiOCl (BOFC) heterojunction was constructed to carry out the photocatalytic PMS oxidation process for tetracyclines (TCs) pollutants at low PMS concentrations (0.08 mM). The photocatalytic PMS oxidation rate of Bi25FeO40/BiOCl composites for tetracycline hydrochloride (TCH), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) reaches 86.6%, 83.6%, 86.7%, and 88.0% within 120 min. Simultaneously, the BOFC/PMS system under visible light (Vis) equally displayed the practical application prospects for the solo and mixed simulated TCs antibiotics wastewater. Based on the electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) valence band spectrum, a Z-scheme electron migration pathway was proposed to elucidate the mechanism underlying the performance enhancement of BOFC composites. Bi25FeO40 in BOFC composites can serve as active site for activating PMS by the formation of Fe3+/Fe2+ cycle. Toxicity estimation software tool (T.E.S.T.) and mung beans planting experiment demonstrates that BOFC/PMS/Vis system can reduce toxicity of TCs wastewater. Therefore, BOFC/PMS/Vis system achieves efficient examination in different water environments and efficient utilization of PMS, which displays a scientific reference for achieving environmentally-friendly and resource-saving handling processes.

Photocatalytic Oxidation Process for Petroleum Wastewater Treatment and The Possibility of Using Tapered Bubble Column (TBC): A Review

<p>The photocatalytic oxidation of organic and petroleum wastewater treatment is an advanced oxidation process (AOP) with several benefits. It operates at normal temperatures and pressure, is inexpensive, does not produce secondary waste, and us easily accessible. Many studies have employed bubble columns, slurry bubble columns, and three-phase fluidized reactors in the photocatalytic process for wastewater treatment. Pure TiO2 and Fe-doped TiO2 are considered the most promising catalysts. The aim of this work was to review the literature on the photocatalytic process for organic pollutants and petroleum wastewater (produced water) treatment, with a special focus on pure TiO2 and Fe-doped TiO2 as well as to study the possibility of using a tapered bubble column reactor for this treatment. A circulating upflow tapered bubble column reactor with a light lamp at the center facilitates the separation of the gas-liquid-solid phases with no dead zone in the photocatalytic process.</p>

Cu2O/WO3 S-scheme heterojunctions for photocatalytic degradation of levofloxacin based on coordination activation

Heterogeneous photocatalytic degradation of antibiotic involves the activation of antibiotic molecules and the photocatalytic oxidation process. However, the simultaneous improvement of these processes is still a challenge. Herein, S-scheme heterojunctions consisted of Cu2O nanocluster with defective WO3 nanosheets were constructed for efficient photocatalytic degradation of levofloxacin (LVX). The typical CNS-5 composite (5 wt% Cu2O/WO3) achieves an optimal LVX degradation efficiency of 97.9% within 80 min. The spatial charge separation and enhancement of redox capacity were realized by the formation of S-scheme heterojunction between Cu2O and WO3. Moreover, their interfacial interaction would lead to the loss of lattice oxygen and the generation of W5+ sites. It is witnessed that the C–N of piperazine ring and CO of carboxylic acid in LVX are coordinated with W5+ sites to build the electronic bridge to activate LVX, greatly promoting the further degradation. This work highlights the important role of selective coordination activation cooperated with S-type heterojunctions for the photocatalytic degradation and offers a new view to understand the degradation of antibiotics at molecular level.

Deactivation of porphyrin metal-organic framework in advanced oxidation process: Photobleaching and underlying mechanism

Porphyrin metal-organic frameworks (MOFs) are widely used in photocatalytic advanced oxidation processes (AOP). However, the stability and deactivation of MOFs, crucial for reusability, have been understudied compared to their catalytic activity. We investigated photobleaching in porphyrin MOFs PCN-224-M (M= H2, Fe, Co, Cu, Zn) under visible light and H2O2. The MOFs exhibited crystallinity loss, ring-opening cleavage, and linker degradation. Photobleaching resulted from direct redox reactions between porphyrin sites and H2O2. Metal-oxo-porphyrin intermediates played a key role in the "group effect," with different functional groups affecting the photobleaching rate: PCN-224-Fe ≈ PCN-224-Co > PCN-224-H2 > PCN-224-Cu ≈ PCN-224-Zn. This trend related to chelated metal ions' electronic structures and their propensity for metal-oxo intermediate formation, establishing a structure-stability relationship. Our study enhances understanding of deactivation mechanisms in porphyrin MOFs during AOP, aiding the design of resilient and efficient MOF catalysts for environmental applications.

Photocatalytic Reduction of VOCs with Ag/Ni-Doped Photocatalyst in Different Temperature and Humidity Environments

The photocatalytic oxidation (PCO) process is one of the most preferred, inexpensive, and environmentally friendly methods for VOC removal. It has been determined that this method can remove a wide range of organic pollutants. The removal of benzene and toluene pollutants, two important VOCs commonly encountered in flue gases, has been studied in the scope of this study using the photocatalytic oxidation method under UVA irradiation. For this purpose, the photocatalytic activity of the photocatalyst increased by the metal/metal doping process. Two different metals, a noble metal (Ag) and a transition metal (Ni), were used together for the doping of TiO2 nanoparticles, and the photocatalysts attached to a glass surface were prepared. Four different doping percentages were used for photocatalysts: 0.5%, 1%, 2.5%, and 5%. Several PCO experiments were conducted under different temperatures (120, 150, and 180 °C) and humidity conditions (25 and 50%). Photocatalytic oxidation experiments were carried out with artificially produced benzene and toluene gases, and the success of the system was evaluated with respect to removal efficiency calculations. The UVA light source was used for the photocatalytic experiments. The results of the study indicated that the removal efficiencies of toluene were found to be higher than those of benzene, and the most suitable conditions were determined to be 50% humidity and a 120 °C environment with the use of a 1% doped photocatalyst.

Catalyst-On-Hotspot Nanoarchitecture: Plasmonic Focusing of Light onto Co-Photocatalyst for Efficient Light-To-Chemical Transformation.

Plasmon-mediated catalysis utilizing hybrid photocatalytic ensembles promises effective light-to-chemical transformation, but current approaches suffer from weak electromagnetic field enhancements from polycrystalline and isotropic plasmonic nanoparticles as well as poor utilization of precious co-catalyst. Here, efficient plasmon-mediated catalysis is achieved by introducing a unique catalyst-on-hotspot nanoarchitecture obtained through the strategic positioning of co-photocatalyst onto plasmonic hotspots to concentrate light energy directly at the point-of-reaction. Using environmental remediation as a proof-of-concept application, the catalyst-on-hotspot design (edge-AgOcta@Cu2 O) enhances photocatalytic advanced oxidation processes to achieve superior organic-pollutant degradation at ≈81% albeit having lesser Cu2 O co-photocatalyst than the fully deposited design (full-AgOcta@Cu2 O). Mass-normalized rate constants of edge-AgOcta@Cu2 O reveal up to 20-fold and 3-fold more efficient utilization of Cu2 O and Ag nanoparticles, respectively, compared to full-AgOcta@Cu2 O and standalone catalysts. Moreover, this design also exhibits catalytic performance >4-fold better than emerging hybrid photocatalytic platforms. Mechanistic studies unveil that the light-concentrating effect facilitated by the dense electromagnetic hotspots is crucial to promote the generation and utilization of energetic photocarriers for enhanced catalysis. By enabling the plasmonic focusing of light onto co-photocatalyst at the single-particle level, the unprecedented design offers valuable insights in enhancing light-driven chemical reactions and realizing efficient energy/catalyst utilizations for diverse chemical, environmental, and energy applications.

High-strength, anisotropic bamboo hydrogel via in situ lignin modification for ion-selective transport and sensor

Biomass-based anisotropic hydrogels are severely limited in the practical production and applications due to the weak mechanical properties, time-consuming preparation process and toxic chemical reagents. Herein, a high-strength anisotropic bamboo-based hydrogel is fabricated via in situ lignin modification of natural bamboo and flexibility process, with directionally porous structure and superior mechanical properties. The lignin modification with an UV photocatalytic oxidation process maintains the heterostructure of natural bamboo and exposes polar groups, which provide the bonding sites for subsequent flexibility process. Then, the flexible polyacrylamide (PAM) molecular chains are polymerized in the modified bamboo (photonic bamboo) to construct superior-strength anisotropic bamboo/PAM composite hydrogel (BPCH). The synthesized BPCH has an axial tensile strength (123.5 MPa) and a Young's modulus (3.46 GPa) that significantly outdistance all previous biomass-based hydrogels. Benefiting from the unique porous micro-nanostructure, the BPCH serves as an excellent and stable nanofluidic channel for ion-selective transport and presents the ion conductivity of 5.75 × 10-4 S cm−1 at a low content. Additionally, the BPCH presents stable bending sensitivity to monitor both macroscopic and tiny human actions, such as finger bending, etc. This design offers a high-strength biomass templates and green process for next-generation anisotropic hydrogels, realizing the high value utilization of the bamboo in the micro/nanofluidic and sensor fields.

Construction of novel dual Z-scheme heterojunction of ternary CdS/g-C3N4/NiFe2O4 magnetically retrievable nanocomposite for boosted photocatalytic and energy storage applications

A novel CdS/g-C3N4/NiFe2O4 (CGN) ternary nanocomposite photocatalyst was rationally developed via a simple wet-impregnation technique. Looking at the band structure of the components of the catalyst, a novel dual Z-scheme heterojunction can be successfully developed, generating more active sites that rapidly encourage the separation of the photo-generated species, contributes to preventing the aggregation of the synthesized nanocomposite, and enhance the light absorption efficiency. Remazol Brilliant Blue R (RBBR) was photocatalytically degraded by the nanocomposite in the presence of visible light to assess its photocatalytic effectiveness. The CGN 2 ternary nanocomposite had the maximum photocatalytic activity (96 %) if compared to the other prepared photocatalysts, as the rate of degradation of pure CdS, CdS/g-C3N4, CGN 1, and CGN 3 nanocomposites were only around 53.4, 85, 87.5, and 92 %, respectively, keeping the irradiation time. Based on trapping tests, •OH, •O2− and h+ radicals are the main active species that play a vital role in the photocatalytic oxidation process. Even after the fourth cycle, the CGN 2 composite remained efficient in the successive photocatalytic degradation of RBBR , maintaining over 91 % of its first degradation efficiency. The CdS/g-C3N4/NiFe2O4 nanocomposite revealed outstanding cycling stability due to its inherent magnetic property, making it a promising choice as a visible light photocatalyst. The electrochemical energy-storage behavior of CGN 2 as active electrode material exhibited a remarkable specific capacitance of 195 F g−1 (67 C g−1) at 1 A g−1. It delivered an outstanding cycling stability of 91 % capacity retention after 2000 charge–discharge cycles. The obtained remarkable results indicate that the CGN 2 nanocomposite is a promising active electrode material for high-performance energy-storage supercapacitors.

Predictive modeling for VOC adsorption on TiO2 filters: Implications for enhanced photocatalytic oxidation in indoor air quality management

Adsorption of volatile organic compounds (VOCs) onto the surface of a TiO2 filter is essential for initiating photocatalytic oxidation (PCO). This study investigated the adsorption coefficients (K) of 14 VOCs under different relative humidities (RH) and explored the influence of different air velocities on the adsorption of Methyl isobutyl ketone (MIBK). Consequently, a polyparameter linear free energy relationship (pp-LFER) model was established to predict lnK at 35 % RH (lnK35%). Moreover, the study found that lnK has a linear relationship with RH, represented as lnK=αRH+β. The parameters ′α′ and ′β′ can be accurately predicted using the Henry’s Law constant (K°OH) and lnK35%, respectively. By combining the pp-LFER model with regression equations for ′α′ and ′β′, it is possible to predict lnK for VOCs across various RH levels. The study also revealed that the adsorption coefficient of increases with escalating air velocities (0.04 – 0.34 m/s), primarily due to mass transfer. The observed low adsorption performance for aldehydes, commonly seen as by-products in the PCO process, suggests cautious usage of the PCO filtration system in practice before the by-products are eliminated downstream. This study offers valuable insights for the practical application of PCO technologies in the comprehensive removal of indoor VOCs.

Human Health Risk Assessment of the Photocatalytic Oxidation of BTEX over TiO2/Volcanic Glass.

This study demonstrates rapid photocatalytic oxidation of a benzene, toluene, ethylbenzene, and xylene (BTEX) mixture over TiO2/volcanic glass. The assessment of the photocatalytic oxidation of BTEX was conducted under conditions simulating those found in indoor environments affected by aromatic hydrocarbon release. We show, under UV-A intensities of 15 mW/cm2 and an air flow rate of 55 m3/h, that low ppmv levels of BTEX concentrations can be reduced to below detectable levels. Solid-phase microextraction technique was employed to monitor the levels of BTEX in the test chamber throughout the photocatalytic oxidation, lasting approximately 21 h. Destruction of BTEX from the gas phase was observed in the following sequence: o-xylene, ethylbenzene, toluene, and benzene. This study identified sequential degradation of BTEX, in combination with the stringent regulatory level set for benzene, resulted in the air quality hazard indexes (Total Hazard Index and Hazard Quotient) remaining relatively high during the process of photocatalytic oxidation. In the practical application of photocatalytic purification, it is crucial to account for the slower oxidation kinetics of benzene. This is of particular importance due to not only its extremely low exposure limits, but also due to the classification of benzene as a Group 1 carcinogenic compound by the International Agency for Research on Cancer (IARC). Our study underscores the importance of taking regulatory considerations into account when using photocatalytic purification technology.

Comparative Study of Organics Removal from Refinery Wastewater by Photocatalytic Fenton Reaction Coupled with Visible Light and Ultraviolet Irradiation

The study investigates photocatalytic advanced oxidation processes using iron-doped zeolite catalysts in heterogeneous Fenton reactions to degrade organic contents as chemical oxygen demand. The research revealed that the heterogenous photocatalytic Fenton process was the most successful treatment method under acidic circumstances and generated a greater rate of chemical oxygen demand degradation in a concise amount of radiation time. Compared to the heterogenous Fenton process with ultraviolet irradiation, it increased oxidation and was affected by catalyst load, power of hydrogen pH, hydrogen peroxide amounts, and temperature. The findings showed that the iron-doped zeolite catalyst, pH, and temperature significantly degraded the chemical oxygen demand. The experiment determined that the optimal conditions were obtained at a catalyst load of 0.07 g, pH of 3, with 20% excess of hydrogen peroxide, 40 °C in 2 hours for the ultraviolet/ iron-doped zeolite/hydrogen peroxide system that gave 99.84 % of the removal of the chemical oxygen demand. The heterogeneous photocatalytic Fenton method accompanied the reactions by hydroxyl radical production, which quickly reached its maximal reduction.

Removal of imidacloprid in geopolymer granules coupled with low-intensity photocatalytic and chemical oxidation processes

In this study, TiO2-immobilized geopolymer granules (TiO2-GCs) were developed for the removal of imidacloprid from water. TiO2 nanoparticle immobilization into the geopolymer material helped increase its crystalline structure and refine geopolymer pores by filling up mesopores and macropores (10–100 nm) in the porous geopolymer materials resulting in its denser structure. The maximum TiO2 content for the formation of geopolymer having good structural properties was 14 wt%. Then, the removals of imidacloprid from water through adsorption and photocatalytic processes in the TiO2-GCs were evaluated. The imidacloprid adsorption efficiencies varied between 10.7 and 11.1 % with the increase in TiO2 contents not influencing the imidacloprid adsorption on the TiO2-GCs. After UV irradiation, a maximum removal efficiency of 96.85 % of gradually absorbed imidacloprid on TiO2-GCs was achieved at 14 wt% TiO2 content. The results demonstrated that photocatalytic degradation was the main responsible mechanism for imidacloprid removal. The addition of H2O2 (10–20 mM) increased the imidacloprid removal rates in TiO2-GCs by 30–60 %.

Magnetically separable MnFeCoNiCu-based high entropy alloy nanoparticles for photocatalytic oxidation of antibiotic cocktails in different aqueous matrices

Destroying persistent organic pollutants via photocatalytic advanced oxidation processes is critical for sustainable water management. In spite of the tremendous progress in developing highly effective and durable photocatalysts in recent decades, inferior optical absorption and rapid charge recombination considerably restrict their application on a commercial scale. In order to address these issues, herein we have constructed MnFeCoNiCu-based high entropy alloy (HEA) nanoparticles (NPs), through a facile and straightforward procedure, and showcase its superiority over conventional photocatalysts in degrading some typical antibiotics (viz., sulfamethoxazole, SMX; ofloxacin, OFX; and ciprofloxacin, CFX). The equimolar HEA-NPs feature n-type semiconducting properties, improved light trapping ability, and reduced charge recombination. Consequently, a high degradation of 95 %, 94 %, and 89 % for SMX, OFX, and CFX, respectively, can be achieved in the presence of MnFeCoNiCu NPs under visible light illumination, without any serious risks of secondary contamination. In order to better evaluate the photocatalytic performance of MnFeCoNiCu NPs, particularly from a practical perspective, the removal of antibiotic pollutants from multicomponent systems is also investigated. The average treatment efficiency for a ternary mixture of SMX, OFX, and CFX in different aqueous matrices decreases in the order of deionized water (∼82 %) < tap water (∼86 %) < river water (∼78 %) < hospital wastewater (∼60 %) < domestic wastewater (∼57 %) < pharmaceutical industry wastewater (∼47 %). Further, the expended HEA-NPs can be conveniently recovered from the reaction system by applying an external magnetic field, allowing recurrent usage, without any substantial alteration in their microstructure and performance. These demonstrations of satisfactory photocatalytic activity under a diverse spread of realistic environmental conditions, excellent durability, and inexpensive retrieval endorse the application potential of MnFeCoNiCu NPs in decentralized water treatment systems.

Analysis of a UV photocatalytic oxidation-based disinfection system for hydroxyl radicals, negative air ions generation and their impact on inactivation of pathogenic micro-organisms.

This work presents a large-scale surface disinfection system, which has a unique lantern arrangement of ultraviolet-C (UV-C) light (254nm) in conjunction with nanotechnology in a protective biosafety environment. Shadow regions are best dealt in this system by the generation of hydroxyl radicals (•OH) and negative air ions at sites where UV light cannot penetrate. More than 35 000 negative air ions/cm3 along with •OH were produced continuously in the disinfection chamber through the advanced photocatalytic oxidation process [UV-C + titanium dioxide (TiO2)]. The arrangement has been made to provide an optimized UV irradiation (∼2 mW/cm2) throughout the disinfection system. In order to distinguish between effects arising from (i) the action of UV dose alone and (ii) the action of UV dose along with •OH and negative air ions, E. coli and P. aeruginosa were chosen for bacterial testing and two interventions were made. The first intervention involved placing only UV lamps in the disinfection chamber to see the effect of only UV dose on bacterial inactivation efficiency. The second intervention involved placing the TiO2 nanoparticle coated aluminum plates along with UV lamps; this allows for the generation of negative air ions and •OH inside the disinfection chamber and enhanced bacterial inactivation efficiency. More than 95% bacterial inactivation efficiency has been reported in the case of UV-C + TiO2 compared to only 77% in UV only at the same time interval (90s).