Photocatalytic Degradation Mechanism Research Articles

Synthesis of TiO2-ZnO n-n Heterojunction with Excellent Visible Light-Driven Photodegradation of Tetracycline.

Zinc oxide-based photocatalysts with non-toxicity and low cost are promising candidates for the degradation of tetracycline. Despite the great success achieved in constructing n-n-type ZnO-based heterojunctions for the degradation of tetracycline under full-spectrum conditions, it is still challenging to realize rapid and efficient degradation of tetracycline under visible light using n-n-type ZnO-based heterojunctions, as they are constrained by the quick recombination of electron-hole pairs in ZnO. Here, we report highly efficient and stable n-n-type ZnO-TiO2 heterojunctions under visible light conditions, with a degradation efficiency reaching 97% at 1 h under visible light, which is 1.2 times higher than that of pure zinc oxide, enabled by constructing an n-n-type heterojunction between ZnO and TiO2 to form a built-in electric field. The photocatalytic degradation mechanism of n-n TiO2-ZnO to tetracycline is also proposed in detail. The demonstration of efficient and stable heterojunction-type ZnO photocatalysts under visible light is an important step toward commercialization and opens up new opportunities beyond conventional ZnO technologies, such as composite ZnO catalysts.

One-step synthesis of Z-scheme BiOBr/Bi/BiOI efficient heterojunction photocatalysts and the effect of ascorbic acid

Ternary-component BiOBr/Bi/BiOI composites were successfully prepared by a one-step hydrothermal method under the reducing effect of ascorbic acid. Ascorbic acid not only converts Bi3+ to Bi0 as a reducing agent, but also inhibits the growth of grains and controls the morphology, resulting in a multilayered hierarchical floral structure of the BiOBr/Bi/BiOI composites formed by the assembly of nanosheets dotted with nanoparticles on the surface. The composite has highest photocurrent density, lowest photogenerated electron-hole recombination rate and high specific surface area, and exhibits excellent degradation performance for both single and mixed pollutant systems of tetracycline, rhodamine B and methylene blue. h+ is the most dominant reactive oxygen species in the photodegradation process, while ·OH and ·O2− provide weak auxiliary degradation. A Z-scheme photocatalytic degradation mechanism of BiOBr/Bi/BiOI with excellent photocatalytic performance was proposed.

Core‐shell Structured Nano CuO@CER Composites for the Photoelectrocatalytic Degradation of Methylene Blue

AbstractThe composite material of nano CuO loaded on ion exchange resin (CuO@CER) as the carrier was prepared successfully by constant temperature oscillation and hydrothermal synthesis methods. It was applied to the photoelectrocatalytic degradation of methylene blue (MB) as an organic pollutant, and further to explore the optimal conditions for CuO@CER photoelectrocatalytic degradation of MB. The results showed that the composite material had a typical core‐shell structure, and the nano CuO loaded on the ion exchange resin had good crystallinity and high purity. CuO@CER exhibited excellent photocatalytic and photoelectrocatalytic performance towards MB, with degradation rates of 92.02% and 95.20% in 70 min under their respective optimal reaction conditions. Furthermore, the photoelectrocatalytic stability of CuO@CER was good relatively, and the degradation rates of MB exceeded 96% after 5 cycles of photoelectrocatalytic experiments. Free radical quenching experiments indicated that superoxide radicals were the main active groups during the photoelectrocatalysis. Additionally, the mechanism of photocatalytic degradation for MB under the electric field was briefly analyzed. This study will provide technical support for the photoelectrocatalytic degradation of organic dye wastewater.

The role of process parameters on photooxidative degradation of 2,4-D herbicide using TiO2 nanoparticles: Kinetic and mechanistic study

This systematic study investigates the effect of a wide range of TiO2 nanoparticles on the kinetics and mechanism of photocatalytic degradation of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). Changes in degradation rate, mineralization, and transformation pathways of 2,4-D correlated with nanoparticle physicochemical properties such as phase composition, size, and total pore volume. Primary intermediates, including hydroxylated chlorophenoxyacetic acids and 2,4-dichlorochlorophenoxy derivatives, were identified and their formation yields linked to the acid-base behaviour of 2,4-D. A comparison with homogeneous UV/H2O2-assisted degradation showed similar distribution of hydroxylated aromatic degradation intermediates as with large anatase nanoparticles (70 nm), while smaller particles facilitated pathways leading to the direct 2,4-D mineralization. DFT calculations supported experimental findings, and a scheme of the oxidative degradation of 2,4-D was proposed. Our results demonstrate that monitoring not only pollutant degradation but also overall mineralization is essential for evaluating photocatalysis efficiency and potential for practical applications.

Templates effects on the morphological, optical, and photocatalytic properties of ZnO nanostructures synthesized via precipitation method

A simple and effective method was used to synthesize zinc oxide (ZnO) nanoparticles in the presence of chitosan (Cs) and Pluronic 123 (P) as templates. A comparative study was then conducted to evaluate the optical, morphological, and photocatalytic properties of the resulting materials. The synthesized nanoparticles were characterized using various techniques, including XRD, FTIR, DRS, EDX, SEM, and N2 adsorption–desorption. Additionally, density functional theory (DFT) calculations were employed to explore the electronic properties of the nanoparticles. The results demonstrated that the templates significantly influenced in the morphology of materials. Additionally, ZnO-Cs showed a lower band gap and the highest specific surface area (20.57 m2/g). The samples showed good stability and significant photocatalytic activity under UV-B radiation at the natural solution pH (without adjustment). The degradation of methylene blue (MB) was confirmed by liquid chromatography-mass spectrometry (LC-MS) analysis. Furthermore, the mechanism of photocatalytic degradation of the organic dye was investigated using conceptual DFT analysis and validated through comparison with previously reported experimental data.

Enhancing Microplastic Degradation through Synergistic Photocatalytic and Pretreatment Approaches.

Microplastics (MPs) pollution has emerged as a pressing environmental concern in recent years. Owing to their minute dimensions, conventional plastic remediation approaches are inadequate for addressing the challenges posed by MPs. Herein, spherical (BOC-S) and nanosheet (BOC-N) BiOCl photocatalysts were prepared and applied to the degradation of poly(ethylene terephthalate) (PET) MPs after hydrothermal pretreatment. The results indicated that the degradation efficiency of pretreated PET MPs using BOC-S and BOC-N photocatalysts was 8.8 and 6.9 times that of the unpretreated MPs under the same conditions. Comparative experiments confirmed the excellent performance of the photocatalysis-pretreatment system. The creation of pores on the surface of pretreated PET MPs facilitates the entry of active substances into the interior to cause damage, while the enhancement of hydrophilicity and specific surface area facilitates the contact between the catalyst and PET MPs, thus increasing the degradation efficiency. Free radical trapping experiments revealed that hydroxyl radicals (·OH) produced by photocatalysis had the greatest influence on the degradation performance of pretreated PET MPs. Finally, a possible photocatalytic degradation mechanism for PET MPs was proposed. This research offers a novel perspective on MPs degradation, providing valuable insights for advancing the efficacy of the process.

Enhanced photocatalytic properties of visible light-responsive ZnS/FeWO4 composites for degradation of tetracycline and Escherichia coli inactivation

The development of highly efficient visible light-driven photocatalysts for the removal of diverse pollutants is crucial for wastewater treatment. In this study, a series of ZnS/FeWO4 composites were prepared via a facile hydrothermal method combined with in situ calcination. The photocatalytic properties of the resulting ZnS/FeWO4 composites were evaluated for the degradation of tetracycline (TC) and the inactivation of Escherichia coli (E. coli), considering the environmental persistence and potential carcinogenicity of these pollutants. The optimized ZnS/FeWO4-1:2 photocatalyst demonstrated outstanding activity in the degradation of TC, achieving a degradation efficiency of 91.7 % (k = 0.0230 min⁻¹), which is significantly higher than that of pristine FeWO4 (67.5 %) and ZnS (53.4 %). Kinetic studies confirmed that the degradation process followed a pseudo-first-order kinetic model. Furthermore, the as-prepared photocatalyst exhibited excellent stability after five cycles. Additionally, the ZnS/FeWO4-1:2 composites showed potent inactivation efficiency, achieving approximately 96 % inactivation of 7.0 × 106 CFU/mL E. coli. These superior photocatalytic capabilities are attributed to the effective integration of FeWO4 with ZnS and the formation of optimal heterojunction structures. This incorporation leads to a delay in electron-hole recombination within the nanocomposites. Moreover, the enhancement mechanisms of photocatalytic TC degradation over ZnS/FeWO4-1:2 composites were discussed. The findings of this study provide valuable insights into the multi-application potential of ZnS/FeWO4-1:2 composites and demonstrate an effective approach to designing photocatalysts for wastewater treatment.

Efficiency and mechanistic insights of photocatalytic degradation and sterilization utilizing g-C3N4/WO3-x Z-scheme heterojunction under full-spectrum light

Designing highly efficient full-spectrum responsive Z-scheme heterojunction for wastewater decontamination and disinfection is urgently essential. Herein, a novel Z-scheme g-C3N4/WO3-x heterojunction was successfully synthesized by a facile wet impregnation method for the highly efficient photocatalytic degradation and sterilization. Benefiting from the accelerated charge separation, broadened light absorption to near infrared region, and appropriate band energy, optimized g-C3N4/WO3-x heterojunction exhibited photocatalytic degradation of 86.3 % and 97.4 % tetracycline in 2 h under visible light and full-spectrum light, respectively. Meanwhile, 6.5-log of Escherichia coli strains could also be inactivated by optimized g-C3N4/WO3-x heterojunction within 45 min and 15 min under visible light and full-spectrum light, respectively. Impressively, it also exhibited desirable anti-interference ability and satisfying photocatalytic degradation capacity with various key experimental parameters. The plausible degradation pathways of TC and the main active species involved in the photocatalysis were investigated based on liquid chromatography-mass spectrometer (LC-MS) and electron paramagnetic resonance (EPR) analysis. Mineralization process of TC was further confirmed by three-dimensional fluorescence spectra (3D EMMs). Besides, Toxicity Estimation Software Tool (T.E.S.T.) and Ecological Structure-Activity Relationships (ECOSAR) program were applied to predict the noxiousness of TC and its potential intermediates. The results suggested that the excitotoxicity of intermediates generally decreased relative to the pristine TC. Finally, we propose a plausible enhancement mechanism of photocatalytic degradation and sterilization. This work sheds a new light on the design of novel full-spectrum responsive Z-scheme heterojunction for environmental remediation.

Preparation of Soybean Dreg-Based Biochar@TiO2 Composites and the Photocatalytic Degradation of Aflatoxin B1 Exposed to Simulated Sunlight Irradiation.

Aflatoxin B1 (AFB1) is a highly toxic carcinogen severely harmful to humans and animals. This study fabricated SDB-6-K-9@TiO2 composites via the hydrothermal synthesis method to reduce AFB1. The structural characterization results of the photocatalytic composites showed that TiO2 was successfully loaded onto SDB-6-K-9. The different photocatalytic degradation conditions, photocatalyst kinetics, recycling performance, and photocatalytic degradation mechanism were investigated. Photocatalysis with 6 mg of 4%SDB-6-K-9@TiO2 in a 100 μg/mL AFB1 solution presented a reduction of over 95%, exhibiting excellent performance, high stability, and reusability even after five cycles of photocatalytic experiments. Active species trapping experiments confirmed that holes (h+) played the most critical role. After structural analysis and identification of the photocatalytic degradation products, the photodegradation path and photocatalytic oxidation mechanism of 4%SDB-6-K-9@TiO2 were postulated. The results show a new way to improve TiO2's photocatalytic performance, providing a certain theoretical basis for the effective AFB1 reduction.

Enhanced interface charge transfer through heterostructure coupling of NiO/NiCo2O4 and carbon layer for photocatalysis

Constructing heterogeneous composite materials is a promising strategy for enhancing photocatalytic performance. In this study, the calcination method was employed to coat a carbon layer onto the surface of quartz sand. Additionally, NiO/NiCo2O4 heterostructures were loaded onto the carbon layer to facilitate charge transfer and enhance photo-generated electron yield. The carefully designed QSC@NiO/NiCo2O4 heterojunction possesses an efficient interface charge transfer channel, thereby improving contaminant degradation capacity. The results demonstrated that under 120 min of light exposure, the removal efficiencies for RhB and MB reached 94.75 % and 93.55 %, respectively. After undergoing 5 cycles, both RhB and MB exhibited consistently high elimination rates with values of 83.74 % and 77.42 %, respectively. Furthermore, tapping experiments were conducted to explore the mechanism of photocatalytic degradation.

Recent advances in cadmium sulfide (CdS)-based photocatalysts

Organic compounds from different industries produce a range of problematic pollutants in wastewater. Cadmium sulfide (CdS) based photocatalyst as a typical photocatalytic material, due to its high efficiency and stability, shows great potential in the field of environmental restoration, which has strong visible light absorption, suitable band energy level and excellent electron charge transport performance. Research on degradation of organic pollutants using cadmium sulfide (CdS) based photocatalyst has made significant progress. In order to improve the rate and ability of cadmium sulfide (CdS) based photocatalyst to degrade pollutants, this paper introduces various strategies to modify the shape and structure of photocatalyst to improve its performance. In addition, the reaction conditions were optimized, and the mechanism of photocatalytic degradation was discussed. In conclusion, the research of cadmium sulfide based photocatalysts provides valuable insights for the degradation of organic pollutants and offers hope for future application in ecological environmental protection.

Zeolite-decorated black TiOx quantum dots for photocatalytic degradation of organic cationic dyes under LED light irradiation

Defect engineering is a promising strategy to reduce the band gap of semiconductors, enhancing their photocatalytic activity under visible light by introducing intra-bandgap energy states. Among the materials studied, oxygen-deficient black TiOx stands out due to its potential in photocatalytic reduction and hydrogen evolution. However, the valence band edge maximum (VBM) of TiOx is not thermodynamically favorable for the direct oxidation of water to hydroxyl radicals (H2O/•OH). Although the formation of extensive oxygen vacancies is necessary to extend the light absorption of black TiOx to longer wavelengths, a high density of oxygen vacancies (Ov) significantly shortens the diffusion length of charge carriers within the TiOx, leading to increased recombination of electrons and holes (e-/h+), thereby suppressing photocatalytic activity. To overcome these limitations, confining TiOx particles to the quantum dot (QD) size range and constructing heterojunctions with a secondary phase can substantially improve charge carrier separation and photocatalytic performance. In addition to engineering the electronic structure of composite photocatalysts, the preaccumulation of pollutants and their subsequent degradation is an effective strategy. This method decreases the distance between the adsorbed pollutant and the active sites for reactive oxygen species (ROSs) generation, enhancing the efficiency of the photocatalytic degradation process. In this study, we confined TiOx particles to the quantum dot size range by constructing a heterojunction with H-Beta zeolite, which contains defect-induced energy states within its wide band gap. This type of zeolite is particularly effective in adsorbing cationic azo dyes, facilitating pre-accumulation and degradation. The synthesized catalysts were extensively characterized using HRTEM to determine the average size of the TiOx particles and photoluminescence (PL) analysis to investigate charge carrier separation. Our results demonstrated that while TiOx alone showed negligible degradation efficiency, and no •OH were detected, the QD TiOx/Z4 composite achieved complete oxidation of CV by •OH, as confirmed by TOC analysis. The photocatalytic degradation mechanism was proposed based on these experimental findings. These insights could be of significant interest to researchers exploring defective semiconductors for photocatalytic oxidation of organic pollutants in the liquid phase under visible light (LED) irradiation.

Fabrication of a novel Ag2S-ZnS/ZIF-8 hollow heterojunction by in-situ formation of Ag2S and ZnS on ZIF-8 with enhanced tetracycline degradation performance

Currently, antibiotics are extensively utilized in the pharmaceutical industry to assist humans and animals in combating various infectious diseases. The extensive use of various antibiotics enhances the quality of life. However, it can also have negative effects on the environment and human health, including water pollution and the rise of antibiotic-resistant microorganisms. To date, antibiotics have been detected in rivers, groundwater, and even drinking water. There is an urgent need to design and develop advanced materials for the remediation of antibiotics present in our environment. In this paper, we successfully synthesized a novel Ag2S-ZnS/ZIF-8 hollow heterojunction via facile sulphuration and solvothermal methods. This heterojunction was employed as a catalyst for the degradation of tetracycline (TC) in water under UV and visible light irradiation. The physicochemical properties of the as-synthesized catalysts were thoroughly analyzed using XRD, EDS, SEM, BET, XPS, TEM, ESR, UV–vis techniques. The results demonstrate that Ag2S-ZnS/ZIF-8 displays enhanced photocatalytic activity for TC degradation no matter under visible or UV light irradiation. After 10 min of UV light irradiation, its photocatalytic degradation efficiency was achieved 92.74 %. Additionally, Ag2S-ZnS/ZIF-8 was able to degrade 92.14 % of TC (visible light, with 35 min). The corresponding kinetic rate constant of Ag2S-ZnS/ZIF-8 is 0.145 min−1 (UV light) and 0.043 min−1 (visible light), respectively. Furthermore, Ag2S-ZnS/ZIF-8 also shown excellent stability for the degradation of TC in the presence of visible light. This is a result of its high specific surface area, superior photocurrent and efficient separation of photo-generated electrons-hole pairs. Apart from this, the photocatalytic degradation mechanism of TC over Ag2S-ZnS/ZIF-8 is discussed in detail.

An efficient novel NiCu@INA/rGO MOF hollow microsphere Z-scheme heterojunction catalyst for the photocatalytic degradation of tetracycline and simultaneous degradation of cationic and anionic Dyes

Bimetallic metal-organic framework materials have captivated considerable attention in photocatalysis because of their colossal properties like semiconducting, large surface area, and potent visible light harnessing ability. Self-aggregation and rapid recombination rates have greatly hindered their applications in photocatalysis. A novel reduced graphene oxide-incorporated bimetallic nickel copper metal-organic framework (NiCu@INA/rGO MOF) is fabricated using isonicotinic acid as an organic linker. A synergistic effect between the two metals increased the photocatalytic performance. Introducing reduced graphene oxide to nickel-copper MOF increased charge carrier retention transfer and enhanced the catalyst’s water dispersibility. The efficiency of the photocatalyst for the removal of tetracycline (TCn) and a mixture of Rhodamine B (RhB) and Orange G (OrG) dyes was investigated under visible light. A degradation efficiency of up to 89 % for TCn and close to ∼97.8 % and 93.5 % degradation in the case of RhB and OrG dyes was observed. The studies on the photocatalytic degradation mechanism were explored by conducting radical scavenger experiments, Electron spin resonance (ESR) studies, and Mott-Schottky analysis. TCn and RhB degradation pathways were explored by mass spectral analysis of the intermediates during the photocatalytic degradation of TCn and RhB. This work provides new paradigms for the functional modification of MOF for designing efficient photocatalysis.

Sustainable photodegradation of pharmaceuticals: KOH-impregnated palm oil mill effluent sludge biochar-BiOBr nanocomposite for wastewater treatment

Biochar has explored in the search of a cost-effective and environmentally friendly photocatalyst for the efficient degradation of CIP antibiotic pollutants. Biochar (BC) produced from palm oil mill sludge was used as a base to fabricate biochar-based BiOBr composites by varying the mass ratio of biochar and BiOBr via a hydrothermal route. The optimized composites BBC-1:1 has exhibited the formation of crystal struvture as tetragonal BiOBr with a a significant specific surface of 267 m2/g (BBC-1:1) while incorporating different mass ratios of BC with BiOBr. This composite facilitates the band gap of BiOBr from 2.87 to 2.42 eV and is consistent with the decreasing recombination rate of electron-hole pairs as suggested by UV-Vis DRS and photoluminescence (PL), respectively. Consequently, the synergistic effect of biochar BiOBr leads to a higher degradation efficiency of CIP showing the highest efficiency (97.49 %) and that of pure BiOBr being 55.66 % under optimized conditions. The degradation rate of the BBC-1:1 composite which observed to be 0.0156 min−1 is 3.25 times that of BiOBr (0.0048 min−1). Furthermore, the scavenging experiments confirmed the significant contribution of the active radicals h+ and O2- as the main photoactive species in the photocatalytic degradation of CIP. Consequently, the photocatalytic degradation mechanism was discussed and the reusability test confirmed the high stability of the BBC composites up to 77 % for the seventh cycles. These results show that the BBC composite is suitable for large-scale practical applications as a green photocatalyst.

G-C3N4 coupled with GO accelerates carrier separation via high conductivity for photocatalytic MB degradation

Graphitic carbon nitride (g-C3N4) is widely utilized in photocatalysis due to its responsiveness to visible light, low cost, and non-toxicity. However, its efficiency is limited by factors such as the rapid recombination of photogenerated electron-hole pairs, slow electron transfer rates, and a limited number of active surface sites. In this study, g-C3N4 was synthesized through thermal polymerization, and varying amounts of graphene oxide (GO) were incorporated via physical blending to fabricate composite photocatalysts. The results indicated that the incorporation of GO not only increased the specific surface area and modified the pore size distribution of g-C3N4 but also affected the heptazine ring structure through chemical bonding, thereby enhancing the density of active sites. Photocatalytic degradation experiments with methylene blue (MB) indicated that g-C3N4 containing 2 % GO exhibited photocatalytic activity 2.84 times greater than that of pristine g-C3N4. Kinetic simulations indicated that the Kapp value for the 2 % GO-g-C3N4 composite was 0.00469 min−1, which is 4.34 times higher than that of pure g-C3N4 (0.00108 min−1). Furthermore, this composite maintained high photocatalytic activity after four cycles of reuse. An analysis of the photocatalytic degradation mechanism revealed that the incorporation of GO effectively promoted the separation and transfer of photogenerated electron-hole pairs, enhanced photocurrent density, and improved carrier separation efficiency. Electron spin resonance (ESR) and free radical scavenging experiments confirmed that the primary active species involved in the degradation of MB by the composite photocatalyst were ·O2- and h+. This study presents a novel approach for enhancing the photocatalytic performance of g-C3N4 by modifying its electronic structure and surface properties.

Anchoring gadolinium oxide nanoparticles onto CuInZnS: Efficient photocatalytic tetracycline degradation and mechanism analysis

Photocatalysis technology is one of the potential methods to remit the growing issues of environmental pollution. It is of great significance to rationally design high performance antibiotic wastewater degradation catalysts in the whole pH range. In this experiment, Gd2O3 nanoparticles (GdO NPs) were successfully grown onto CuInZnS (CIZS) by a simple hydrothermal method. The introduction of GdO has obvious effects on the nanosheet thickness of CIZS, which reduces carrier transport distances and improves the active sites number of CIZS. What’s more, the SO4•- absorption and electron transfer ability are also greatly optimized. Under 300 W Xe light, tetracycline can be efficient degraded more than 93 % in the whole pH range, which presents absolute advantage compared to CIZS and GdO. Based on the combination of experimental characterization and density functional theory calculations, the proposed photocatalytic tetracycline degradation pathway and mechanism have been given. Moreover, the results of toxicity analysis proved that the CIZS-GdO catalyst could successfully reduce the toxicity of tetracycline wastewater. This work has reference value for the application of rare earth oxides in the field of photocatalysis at full pH range.

Novel Br-doped Bi2WO6 photocatalyst for high-efficiency removal of norfloxacin: mechanism and photocatalytic activity.

In this work, the bismuth tungstate (Bi2WO6) photocatalyst was successfully prepared, and the pure Bi2WO6 was modified with Br (Br-Bi2WO6). The effects of different experimental conditions on the degradation of norfloxacin (NOR) solution under visible light were investigated. The Br-Bi2WO6 photocatalyst was characterized by FTIR, XRD, SEM, BET, XPS, DRS, EIS, and EPR. The results show that the Br-modified Bi2WO6 photocatalyst can effectively improve the photocatalytic performance. The best photocatalytic performance of Br-Bi2WO6 was observed when the doping amount of Br was 3%. The degradation percentage of norfloxacin can reach 94.67%. The presence of anions and cations (Cl-, SO42-, Ag+, and Cu2+) in the solution significantly inhibited the photocatalytic activity of 3%Br-Bi2WO6. The photocatalytic degradation of norfloxacin by 3%Br-Bi2WO6 was not greatly affected in the presence of HCO3- and NO3-. The characterization analysis showed that Br was successfully doped on the Bi2WO6 photocatalyst, and the original structure of Bi2WO6 was not destroyed by the addition of Br. Br doping increased the specific surface area of Bi2WO6 and decreased the band gap of Bi2WO6 resulting in a broader visible light absorption range. In addition, Br doping promoted the migration rate of photogenerated electron-hole pairs. The ·O2- and h+ played a major role in the photodegradation of norfloxacin, and the mechanism of photocatalytic degradation of norfloxacin by Br-Bi2WO6 was proposed.

Synthesis of leek-based N,S self-doped CQDs/TiO2 and its application in the photocatalytic degradation of organic pollutants

In this work, N,S self-doped CQDs (N,S-CQDs/TiO2) were synthesized from leeks via a microwave method, and a new leek-based N,S-CQDs/TiO2 composite photocatalytic material was prepared by roasting. The structural characteristics, optical properties, and electrical properties of the N,S-CQDs/TiO2 composites were characterized by Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray powder diffraction (XRD), Solid ultraviolet–visible diffuse reflectance (UV–vis-DRS), Fourier transform infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transient photocurrent response, and Electrochemical impedance spectroscopy (EIS). In addition, the catalytic degradation effect of N,S-CQDs/TiO2 was evaluated by the photocatalytic degradation of Rhodamine B (RhB) and ibuprofen (IBU). The experimental results showed that the photocatalytic degradation effect of leek-based N,S-CQDs/TiO2 was significantly better than that of TiO2, and N,S-CQDs/TiO2 with 1.86 wt% N,S-CQDs (1.86-N,S-CQDs/TiO2), which demonstrated optimal photocatalytic degradation. The photocatalytic degradation rate of RhB (20 mg/L) was 94.65 % within 120 min of high-voltage mercury lamp irradiation, which was 41.15 % higher than that of TiO2(53.50 %), and the degradation rate was 80.10 % after four cycles. After 180 min, the photocatalytic degradation rate of IBU (10 mg/L) was 96.92 %, which was 26.39 % higher than that of TiO2 (70.53 %), and the degradation rate could still reach 78.94 % after four cycles. In this work, the photocatalytic degradation mechanisms of RhB and IBU by N,S-CQDs/TiO2 were explored by free radical capture and ESR free radical detection experiments. This study may serve as an important reference for enhancing the photocatalytic degradation effect by using biomass self-doped CQDs/TiO2 composite photocatalytic materials, and as a reference for the photocatalytic treatment of organic pollutants in water.

Solar-driven remediation of antibiotics in synthetic and real reverse osmosis brine: Addressing lattice oxygen demand and electron transfer for improved purification

This study investigated the significance of integrated advanced oxidation process with reverse osmosis (RO) to ensure the purification and elimination of micropollutants, primarily pharmaceuticals prior to the discharge of brine to the environment. To envisage this, TiO2 based solar driven photocatalysis was employed, highlighting the crucial role of oxygen vacancy formation in the lattice of TiO2 for enhancing the purification of antibiotic contaminants from RO brine. The study elucidated how variations in oxygen environments such as oxygen rich yellow TiO2 (Y-TiO2) and oxygen vacancy black TiO2 (B-TiO2) influence photodegradation reaction kinetics taking ofloxacin (OFX) and tetracycline (TC) as model pollutants. The B-TiO2 exhibited 8.5 times higher photodegradation for OFX compared to Y-TiO2, proving significance in tuning of oxygen environment in lattice. The photodegradation efficiency plot showcases B-TiO2′s efficacy, demonstrating 99.8 % and 99.4 % for OFX and TC, respectively. Additionally, the study investigated the photocatalytic degradation mechanism, identifying predominant charge carriers and reactive species involved, while also assessing the durability of photodegradation processes. The impact of pH on the photocatalytic performance of B-TiO2 in degrading antibiotics explored, spanning pH levels from 2.5 to 10.5. An exploration on band alignment formation in B-TiO2 explains the effectiveness of it over Y-TiO2. Lastly, efficacy of B-TiO2 in degrading antibiotics in real RO brine with high level of salinity (60,200 ppm TDS) is demonstrated, which resulted with photodegradation efficiency of 31.25 % for OFX and 67.8 % for TC, proving applicability of integrated system as a sustainable purification approach. Moreover, the blockage of chloride ions quenching demonstrated improvements in photodegradation emphasizing the influence of chloride ions in high saline conditions.