Single Photocatalysis Research Articles

Photocatalysis coupled electro-Fenton process for treatment of acrylamide wastewater: an optimised study

ABSTRACT Electro-Fenton is a commonly used approach for pollutant removal from different wastewater that requires high energy consumption. Coupling electro-Fenton with solar energy could potentially overcome high power consumption. Thus, this study combined photocatalysis with three-dimensional electro-Fenton to treat acrylamide (AM) wastewater. The removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH3−N), and total organic carbon (TOC) in photocatalysis-coupled electro-Fenton were studied. The effects of current density, iron powder dosage, plate spacing, and photocatalyst dosage on COD and NH3−N removal were also optimised using response surface methodology (RSM). The photocatalysis coupled three-dimensional electro-Fenton reduced energy consumption compared to single photocatalysis or electro-Fenton technology. The COD and NH3−N removal rates were 82.444% and 92.810%, respectively, at the current density of 16.000 mA/cm2, iron powder dosage of 1.330 g, plate spacing of 16.643 mm, photocatalyst dosage of 0.2 g. This study demonstrated that organic pollutants can be degraded efficiently at a low concentration of catalysts coupled with the electro-Fenton process, offering a low-energy consumption treatment of wastewater.

In-situ Fe–O co-doped carbon nitride heterogenous catalyst for enhanced photo-Fenton oxidation performance towards recalcitrant organic pollutants

One-step and in-situ FeCl3-participated molten urea thermal polymerization strategy is designed to prepare Fe–O co-doped carbon nitride photo-Fenton catalyst (Fe/OCN). Fe/OCN exhibits remarkable photo-Fenton catalytic oxidation capacity towards recalcitrant organic pollutants, in which 0.31 wt% Fe/OCN with optimal Fe-doping level exhibits significantly 60 and 6.3 times higher pseudo-first-order kinetic constant than single photocatalysis and Fenton system in the degradation of methyl orange. The enhancement of photo-Fenton catalytic performance is mainly ascribed to the realization of ideal Fe–O and Fe–N coordination structure in the framework of polymeric carbon nitride, which can not only serve as prime sites for the adsorption of target pollutants molecules and transfer channels for directed migration of photogenerated charges, but also well-modulate electronic structure and band structure of Fe/OCN. Accordingly, the resulting boosted charge carriers separation and transfer dynamics and increased electron density around Fe active centers facilitate ≡Fe(II) regeneration and H2O2 activation, leading to the significant production of plentiful reactive species responsible for degradation and mineralization of organic pollutants. The present work provides new insight into the optimized design and precise regulation of carbon nitride-based photo-Fenton system for advanced wastewater treatment.

The synergistic enhancement of photocatalytic activity by Fe3O4–TiO2 nanosheets for rhodamine B degradation

As an advanced oxidation material, Fe3O4-TiO2 nanocomposites have been widely used in wastewater treatment. However, conventional Fe3O4 nanoparticles suffer from drawbacks such as carrier recombination and aggregation, which seriously affect the catalytic activity. In this study, Fe3O4-TiO2 nanosheets with different TiO2 loading rates were synthesized by sol-gel method and solvothermal method. The unique two-dimensional nanostructure of Fe3O4 nanosheets facilitated the deposition of TiO2 nanoparticles, resulting in Fe3O4-TiO2 nanosheets with a high BET specific surface area of 121.67 m2·g−1. Under optimal experimental conditions, the degradation rate of RhB dye in the photocatalytic synergistic Fenton-like system constructed with Fe3O4-TiO2 nanosheets reached 98.12 % within 120 min, significantly surpassing that of single photocatalysis and Fenton-like systems. It was attributed to the unique surface structure of Fe3O4 nanosheets, which provided a larger contact area for TiO2 nanoparticles. It facilitated the effective reduction of Fe3+ to Fe2+ by photogenerated electrons in TiO2, inhibited the recombination of photogenerated electron-hole pairs, and consequently enhanced the degradation rate of RhB dye. Furthermore, Fe3O4-TiO2 magnetic nanosheets exhibited excellent reusability and stability, with the recovery rate and degradation rate of RhB dye remaining above 90 % even after five cycles. More importantly, the catalytic mechanism of Fe3O4-TiO2 nanosheets was elucidated, and •OH identified as the primary reactive species responsible for degrading RhB dye. This work provides a novel research direction for designing and preparing advanced catalytic degradation materials, offering a practical solution to the challenging issue of wastewater treatment.

Enhanced scavenger-free photocatalysis-self-Fenton degradation performance over B-doped NVs modified g-C3N4 via promoting Fe(II)/Fe(III) cycle

As an advanced oxidation method, Fenton oxidation has been extensively studied in industrial wastewater treatment. However, its drawbacks such as high reagent dosage, costliness, and the generation of secondary pollutants have limited its application in urban sewage treatment. Photocatalytic in-situ hydrogen peroxide (H2O2) generation and the construction of photocatalysis-self-Fenton oxidation system (PSFs) is considered a potential approach for applying Fenton oxidation in the sewage treatment industry. In this paper, a nitrogen vacancy-modified B-doped g-C3N4 photocatalyst with high efficiency of H2O2 production without adding a scavenger was prepared based on ion-doping and defect construction. Combined with both characterization analysis and theoretical calculation, it was clarified that the modified catalyst enhanced the photo-generated charge separation and transfer. A PSFs was constructed by adding Fe2+ for the degradation of tetracycline (TC). The system produced H2O2 in-situ through photocatalytic action and promoted the Fe2+/Fe3+ cycle under the action of photo-generated electrons. The system achieved almost complete degradation of TC under the joint action of hydroxyl radicals and superoxide radicals, and maintained more than 90 % degradation efficiency after five cycles. And the efficiency of PSFs was significantly improved compared with that of single photocatalysis and photo-Fenton oxidation.

Removal of metronidazole using a novel ZnO–CoFe2O4@Biochar heterostructure composite in an intimately coupled photocatalysis and biodegradation system under visible light

The intimate coupling of photocatalysis and biodegradation (ICPB) technology has received much attraction because of the advantages of both photocatalytic reaction and biological treatment. In this study, ZnO–CoFe2O4@BC (ZCFC) with p-n heterojunction was prepared and used in an ICPB system to degrade metronidazole (MNZ) wastewater. The microstructure, morphology, and optical behavior of heterojunctions in ZCFC were investigated using SEM, XRD, UV–vis, FTIR, and XPS techniques. The results showed that ZCFC inherited the advantages of bamboo biochar's large pore size, and its large pore structure could provide a habitat for bacterial colonization in ICPB, thus shortening the internal mass transfer distance. The degradation of MNZ and chemical oxygen demand (COD) by the ICPB system was 86.8% and 58.5%, respectively, which was superior to single photocatalysis (72.5% for MNZ and 43.8% for COD) and single biodegradation (23.5% for MNZ and 20.1% for COD). In ICPB, photocatalysis and biodegradation showed a synergistic effect in the removal of MNZ, and the order of the major reactive oxygen species (ROS) leading to reduced toxicity of MNZ to the biofilm was •OH > h+ > O2•-. High-throughput sequencing analysis showed continuous evolution of biofilm structures in ICPB enriched a variety of functional species, among which the electroactive bacteria Alcaligenes and Brevundimonas played an important role in the degradation of MNZ. In this study, we investigated the possible mechanism of photocatalytic and microbial synergistic degradation of MNZ in the ICPB system and proposed a new technology for degrading antibiotic wastewater that combines the advantages of photocatalysis and biodegradation.

Construction of PVDF-HKUST-1/BiVO4 hybrid electrospun flexible fiber membrane for enhanced piezo-photocatalytic reduction performance of Cr(VI)

For the practical implementation of Cr(Ⅵ) removal, effective and recyclable water treatment technology is essential. Polarized electric fields inside piezoelectric materials have proved to be a promising technique for facilitating photogenerated charge separation. In this work, Z-scheme heterojunction photocatalyst HKUST-1/BiVO4 and organic piezoelectric material PVDF were combined through electrospinning to create a novel flexible fiber PVDF-HKUST-1/BiVO4 (PVDF-HV) piezo-photocatalyst membrane. When the amount of HKUST-1/BiVO4 powder was 2.4% and the diameter of the obtained fiber film was 10 cm, the optimal reduction efficiency can be achieved by the piezoelectric photocatalytic reduction in solution with initial pH=2, and the piezo-photocatalytic efficiency of PVDF-HV reached up to 85.33% within 120 min, which was about 1.35 times and 2.19 times greater than that of single photocatalysis and piezoelectric catalysis, respectively. It successfully promoted photo charge separation based on the piezoelectric field in PVDF and the heterojunction produced between HKUST-1 and BiVO4. This research developed an efficient strategy for multi-path collection and exploitation of natural solar energy and vibration energy to boost photoactivity.

Improved piezo-photocatalysis for aquatic multi-pollutant removal via BiOBr/BaTiO3 heterojunction construction

Piezo-catalysis is a green and effective method for degrading rich and obstinate molecules in wastewater. Yet, the piezo-catalytic performance of frequently-used barium titanate (BTO) is still limited for practical applications, thus it is crucial to construct high-efficiency BTO-based catalysts. Herein, BiOBr/BTO heterojunction-based piezo-photocatalysts were successfully prepared using the chemical precipitation method, and an internal electric field was established via ultrasound to promote the separation of photogenerated electron-hole pairs through the synergistic effect of piezocatalysis and photocatalysis. Transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy were utilized to characterize the heterojunction. The degradation performance of Rhodamine B (RhB) by BiOBr/BTO is the best among various pollutants, giving a reaction rate constant up to 20.839 × 10−2 min−1, exceeding numerous previously reported catalysts. In addition, the piezo-photocatalytic reaction rate of BiOBr/BTO for Methyl Orange was 9.298 × 10−2 min−1, ≈ 3.3 times than those of pure BTO (2.806 × 10−2 min−1), and also ≈ 15.9 times and 3.3 times than those of single photocatalysis (0.585 × 10−2 min−1) or piezocatalysis (2.848 × 10−2 min−1). Importantly, the BiOBr/BTO heterojunction demonstrates excellent catalytic degradation performance for a broad range of pollutants (e.g., dyes and antibiotics) and their mixtures, as well as favorable cycling stability and repeatability with changed environmental conditions, displaying applicability in actual wastewater treatment. The possible degradation pathways of RhB were analyzed by liquid chromatography-mass spectrometry. The present work supplies a feasible strategy for the preparation of high-efficiency piezo-photocatalytic BTO-based heterojunctions, which can guide other composites for environmental remediation.

Enhanced Catalytic Performance of Ag NP/0.95AgNbO3-0.05LiTaO3 Heterojunction from the Combination of Surface Plasma Resonance Effect and Piezoelectric Effect Using Facile Mechanical Milling.

An internal built electric field can suppress the recombination of electron-hole pairs and distinctly enhance the catalytic activity of a photocatalyst. Novel t-Ag/0.95AgNbO3-0.05LiTaO3 heterojunction was prepared by reducing silver nanoparticles (Ag NPs) on the surface of the piezoelectric powder 0.95AgNbO3-0.05LiTaO3 (0.05-ANLT) using a simple mechanical milling method. The effects of milling time and excitation source used for the degradation of organic dye by heterojunction catalysts were investigated. The results demonstrate that the optimized 1.5-Ag/0.05-ANLT heterojunction removes 97% RhB within 40 min, which is 7.8 times higher than that of single piezoelectric catalysis and 25.4 times higher than that of single photocatalysis. The significant enhancement of photocatalytic activity can be attributed to the synergistic coupling of the surface plasmon resonance (SPR) effect and the piezoelectric effect.

In situ co-crystallization synthesis of the direct Z-scheme Bi5O7I/Bi2SiO5 heterojunction for enhanced photocatalytic rhodamine B and ciprofloxacin degradation

Semiconductor photocatalysis has driven considerable interests for its desirable potential to tackle the worldwide energy shortage and environmental pollution. In this paper, a novel Bi5O7I/Bi2SiO5 Z-scheme heterojunction photocatalyst was in situ synthesized via a co-crystallization process and partial anion exchange strategy. The XRD and FT-IR pattern validated the successful preparation of the heterojunction. The optimal Bi5O7I/Bi2SiO5 heterojunction displayed an excellent photocatalytic activity towards the ciprofloxacin under the simulated solar light, and the rate constant (0.46021 h−1) was 2 and 7.8 times higher than that of pure BiOI (0.22967 h−1) and Bi2SiO5 (0.05877 h−1). Similarly, the degradation efficiency on rhodamine B (RhB) reached 94%, which was much higher than that of the single photocatalysis. The enhanced photocatalytic performance of the heterojunction photocatalyst could be attributed to the formation of the direct Z-scheme heterojunction between the Bi5O7I and Bi2SiO5, which was favorable for retarding the recombination of photoinduced electron-hole pairs. Moreover, the bacteriostatic activity testing illustrated the toxicity of drug solutions decreased sharply after the photocatalytic degradation with the Bi5O7I/Bi2SiO5-3. The ESR characterization analysis and the free radical trapping experiments synergistically determined the Z-scheme electron transfer path of the heterojunction. The possible photocatalytic mechanism of Bi5O7I/Bi2SiO5 heterojunction was proposed. Overall, the well-designed Bi5O7I/Bi2SiO5 heterojunction depicted great practical promise in efficient treatment of organic pollutants.

Theoretical and experimental elucidation of synergistic enhanced piezo-photocatalysis and mechanism of BiVO4 for organic pollutant degradation

Herein, we have synthesized BiVO4 (BVO) square bricks and spherical particles to elucidate the piezo-photocatalytic performance and involved synergistic mechanism. The photocatalytic, piezocatalytic and piezo-photocatalytic experiments were carried out under irradiation of simulated sunlight, ultrasonic wave and both of them, respectively. The degradation of methylene blue (MB) reveals that, for both BVO bricks and particles, the piezo-photocatalysis is greater than single photocatalysis and piezocatalysis, obviously manifesting a synergistic piezo-photocatalytic behavior according to the "1 + 1 > 2″ principle. The BVO bricks exhibit a higher synergistic effect than spherical particles, which is mainly due to the fact that photoexcited carriers in the square bricks can be directionally forced, by ultrasonic-induced polarization field, to specific surfaces. Density functional theory (DFT) calculation combined with finite-element method (FEM) simulation was performed to elucidate the piezo-photocatalytic mechanism of BVO. Moreover, the degradation pathways of MB and toxicities of degradation intermediates were analyzed.

Synergetic piezo-photocatalytic effect in NaNbO3/WO3 photocatalyst for RhB degradation

Improving the separation efficiency of photo-generated charge carriers is an important strategy to enhance the photocatalytic performance. In this paper, the NaNbO3/WO3 composite photocatalyst was prepared via a hydrothermal method, which exhibited a substantial increase in photocatalytic activity through the synergetic effect of visible light irradiation and ultrasound vibration. The XRD, FT-IR, Raman, SEM, XPS, UV–vis DRS, and photoluminescence spectroscopy results indicated that a large number of WO3 particles were tightly attached to the surface of NaNbO3 nanowires in the NaNbO3/WO3 composite catalyst. Under the piezo-photocatalysis condition, the degradation efficiency of Rhodamine B (RhB) by 5 % NaNbO3/WO3 was significantly improved, reaching 73.7 % within 120 min. Meanwhile, the piezo-photocatalytic degradation efficiency of the NaNbO3/WO3 composite catalyst was increased by 30.1 % compared to single photocatalysis, and the corresponding reaction rate constant (K) was 2.23 times than that of single photocatalysis. In addition, quenching tests showed that h+ was the primary active species in piezo-photocatalytic process. The significant enhancement of piezo-photocatalytic performance was attributed to the piezoelectric field caused by the bending deformation of the NaNbO3 nanowires, which was an important driving force for photo-generated charge carrier separation. Furthermore, the production of multiple redox active sites simultaneously improved the photocatalytic performance.

Coupling FeMgAl-LDH and sludge biofilm for simultaneous and effective removal of nitrate and ammonium in water

The existence of redundant nitrate (NO3−) and ammonium (NH4+) in water caused negative impacts on the ecosystem's stability while the simultaneous removal of these nitrogenous substances has become a challenging task. The intimately coupled photocatalysis and biodegradation (ICPB) system has shown great potential in the efficient removal of aquatic pollutants. In this study, the FeMgAl layered double hydroxide (FeMgAl-LDH) capable of removing NO3− and NH4+ concurrently through adsorption and photocatalysis was successfully synthesized based on the hydrothermal method. The characterization of the material has verified its lamellar structure and the inclusion of metal oxide phases. Then, the ICPB system was constructed by coupling FeMgAl-LDH and biofilm from activated sludge onto a polyurethane carrier. After 12-hour water treatment, the ICPB system could realize 54.45 % and 42.57 % of the NO3− and NH4+ removal rates at a pH of 7 and dissolved oxygen (DO) of 2 mg/L, which was superior to the single photocatalysis and biological treatment. The removal performances of the ICPB system under different pH and DO levels were assayed. Meanwhile, microbial activities, community variation, and relational genes were studied to analyze the microbial mechanisms. The microorganisms in the ICPB system possessed high activity to form extracellular polymeric substances (EPSs), nitrogen transformation, and electron transfer. In all, this study constructed a new ICPB system and revealed its mechanism to simultaneously remove the NO3− and NH4+ from the water.

A step closer to real practice: Integrated tandem photocatalysis-biofilm process towards degradation of crude oil

Intimately coupled photocatalysis and biodegradation (ICPB) systems represent a promising wastewater treatment technology. The implementation of ICPB systems for oil spill treatment is a pressing concern. In this study, we developed an ICPB system comprising BiOBr/modified g-C3N4 (M-CN) and biofilms for the treatment of oil spills. The results demonstrate that the ICPB system achieved the rapid degradation of crude oil, outperforming the single photocatalysis and biodegradation methods by degrading 89.08 ± 5.36% within 48 h. The combination of BiOBr and M-CN formed a Z-scheme heterojunction structure, enhancing the redox capacity. The interaction between the holes (h+) and the negative charge on the biofilm surface promoted the separation of electrons (e−) and h+, thereby accelerating the degradation process of crude oil. Moreover, ICPB system maintained an excellent degradation ratio after three cycles and its biofilms progressively adapted to the adverse effects of crude oil and light. The microbial community structure remained stable throughout the degradation of crude oil, with Acinetobacter and Sphingobium identified as the dominant genera in biofilms. The proliferation of the Acinetobacter genus appeared to be the main factor contributing to the promotion of crude oil degradation. Our work demonstrates that the integrated tandem strategies perhaps represent a feasible pathway toward practical crude oil degradation.

Ultrathin Bi4O5I2 nanosheets as an integrated piezo-photocatalyst: Super visible-light piezo-photocatalysis and synergistic catalytic mechanism

Coupling piezocatalysis in the process of photocatalysis has aroused great interests of researchers to depress the serious recombination of photogenerated charge carriers. However, it still suffers from the inefficient catalytic activity and lacks in-depth understanding on their relationship. In this work, we report that outstanding piezo-photocatalytic activity is achieved over ultrathin Bi4O5I2 nanosheets, and disclose the synergistic catalytic mechanism. Piezoelectric force microscopy (PFM) and COMSOL simulation analysis reveal the strong piezoelectricity of the Bi4O5I2. Under simultaneous irradiation of visible light and ultrasonic, Bi4O5I2 ultrathin nanosheets exhibit a piezo-photocatalytic efficiency of tetracycline hydrochloride (TH) degradation of 88.3% within 8 min with a rate coefficient of 0.4703 min−1, which is 2.3-fold of the sum of the single photocatalysis and piezocatalysis, also far exceeding that of other previously reported piezo-photocatalyst. In situ electrochemical and electron paramagnetic resonance (EPR) under light, ultrasonic, and simultaneous light and ultrasonic conditions disclose that the synergistically enhanced charge separation and transfer and evolution of reactive species (superoxide radicals and holes) occur in the piezo-photocatalytic reaction process, which is derived from the piezoelectric field and band bending. This work emphasizes the effect of the piezoelectric field on strengthening the photocatalytic performance and further the understanding on synergistic piezo-photocatalytic mechanism.

Fe3O4 quantum dots mediated P-g-C3N4/BiOI as an efficient and recyclable Z-scheme photo-Fenton catalyst for tetracycline degradation and bacterial inactivation

Photo-Fenton technology integrated by photocatalysis and Fenton reaction is a favorable strategy for water remediation. Nevertheless, the development of visible-light-assisted efficient and recyclable photo-Fenton catalysts still faces challenges. This study successfully constructed a novel separable Z-scheme P-g-C3N4/Fe3O4QDs/BiOI (PCN/FOQDs/BOI) heterojunction via in-situ deposition method. The results showed that the photo-Fenton degradation efficiency for tetracycline over optimal ternary catalyst reached 96.5% within 40 min at visible illumination, which was 7.1 and 9.6 times higher than its single photocatalysis and Fenton system, respectively. Moreover, PCN/FOQDs/BOI possessed excellent photo-Fenton antibacterial activity, which could completely inactivate 108 CFU·mL−1 of E. coli and S. aureus within 20 and 40 min, respectively. Theoretical calculation and in-situ characterization revealed that the enhanced catalysis behavior resulted from the FOQDs mediated Z-scheme electronic system, which not only facilitated photocreated carrier separation of PCN and BOI while maintaining maximum redox capacity, but also accelerated H2O2 activation and Fe3+/Fe2+ cycle, thus synergistically forming more active species in system. Additionally, PCN/FOQDs/BOI/Vis/H2O2 system displayed extensive adaptability at pH range of 3–11, removal universality for various organic pollutants and attractive magnetic separation property. This work would provide an inspiration for design of efficient and multifunctional Z-scheme photo-Fenton catalyst in water purification.

PPCPs abatement using TiO2-based catalysts by photocatalytic oxidation and ozonation: The effect of nitrogen and cerium loads on the degradation performance and toxicity impact

Pharmaceutical and personal care products (PPCPs) have been consumed in great extension and most of these are found in water bodies, owing to the inefficiency of conventional wastewater treatments. To face against these recalcitrant contaminants, advanced oxidation processes such as photocatalysis and ozonation have been studied. Moreover, the combination of these technologies can improve the degradation of PPCPs, reducing the ozone consumption and the effluent toxicity with the presence of photocatalysts. In particular, this study aimed to evaluate the effects of different N and Ce loads in co-doping TiO2 catalysts on the efficiency of photocatalytic oxidation and photocatalytic ozonation for PPCPs abatement, as well as on the resultant toxicity to aquatic species. Different radiation sources (UVA and solar radiation) were considered for the photocatalytic oxidation. A mixture of 5 PPCPs: paracetamol, sulfamethoxazole, carbamazepine, methylparaben and propylparaben was used as a model synthetic effluent. Photocatalysis showed a low efficiency on the PPCPs removal (<20 %), which was not affected by the radiation source. In general, the tested catalysts showed no or low added-value for reducing the toxicity of the synthetic effluent. Concerning photocatalytic ozonation, the lowest N amount (2.5 % w/w) promoted the best results for PPCPs removal, achieving values up to 100 % with significant reduction of ozone dose compared to photolytic ozonation. In general, photocatalytic ozonation showed better ecotoxicological performance than single photocatalysis. Compared to single photolytic ozonation, a benefitial effect was observed for two aquatic species, using a specific catalyst. This catalyst, prepared by doping TiO2 with 2.5 % w/w N and 1.2 % w/w Ce, showed to be the most promisong one, with potential to be used in photocatalytic ozonation. Hence, this work highlights the potential role of N and Ce co-doped TiO2-based catalysts in photocatalytic ozonation for wastewater treatment.

Chlorine dioxide bleaching wastewater degradation in intimately coupled photocatalysis and functional bacteria: The roles of adsorption, photocatalysis, and biotransformation

Chlorine dioxide (ClO2) bleaching wastewater from bagasse brings a threat to human health. The intimate coupling of photocatalysis and biodegradation (ICPB) as a prospective green technique can remove environmental pollutants. Therefore, this study innovatively integrates functional bacteria with the ICPB system (ICPFB) and discusses the degradation mechanism, pathway, kinetic model, and microbial response behavior of the system to wastewater. The results show that the ICPFB system can simultaneously remove 95% absorbable organic halogen (AOX), 91% COD and 85% dissolved organic carbon (DOC), outperforming single photocatalysis (AOX 72%, COD 80%, DOC 68%) and biodegradation (AOX 41.4%, COD 66%, DOC 45%). Meanwhile, the reaction kinetics model of the ICPFB system is dC/dt = -KC1.22. According to the GC-MS analysis of degradation products, the degradation of organic compounds in wastewater involves gradual dechlorination and aromatic ring opening. Lastly, the Biofilm analysis shows that the functional bacteria possess abilities of dechlorination, aromatic ring opening and carbon oxidation.

Activation of Na2S2O8 by MIL-101(Fe)/MoS2 composite for the degradation of tetracycline with visible light assistance

In this paper, MIL-101(Fe) and MoS2 composites (MIL-101(Fe)/MoS2) were synthesized using a facile solvothermal method. As a new degradation system, the synthesized composites were investigated using persulfate (PS) activation based on visible light (Vis). To establish the superiority of a heterogeneous photochemical catalysis system, the MIL-101(Fe)/MoS2 was used as the catalyst in the presence of Na2S2O8 with visible light irradiation. In the system mentioned, the MIL-101(Fe)/MoS2 catalyst presented a much better catalytic ability than that of either a single photocatalysis or chemocatalysis system. The better catalytic ability suggests that the MIL-101(Fe)/MoS2 catalyst was capable of effectively integrating photocatalysis and chemocatalysis leading to the highest degradation efficiency of 85% in 40 min with tetracycline as the target pollutant. The catalytic system MIL-101(Fe)/MoS2/PS/Vis degraded TC pollutant by forming species of O2‾, 1O2, hydroxyl radicals (•OH) and sulfate radicals (•SO4‾) to degrade TC. Furthermore, the MIL-101(Fe)/MoS2 catalyst displayed better catalytic performance compared to those materials that were previously reported, as verified by the good stability (reached 80% after three cycles) and the high TC degradation rate (85%) of the currently developed material. This system may be applicable to the degradation of TC and other challenging organic pollutants.

A novel strategy to enhance the visible light driven photocatalytic activity of CuBi2O4 through its piezoelectric response

Piezocatalysis is realized in hydrothermally-derived CuBi2O4 nanorods for the first time. Through bi-harvesting of photo- and vibration energies, 98.1% Rhodamine B (RhB) can be degraded, which is significantly higher than ∼38.7% from single photocatalysis and ∼72.8% from single piezocatalysis. The enhanced catalytic activity is attributed to the intensified separation of electron-hole under the piezoelectric potential. Results show that CuBi2O4 is promising catalyst to decompose the organic pollutant in nature water.

Non-woven cotton fabric based intimately coupling of photocatalysis and biodegradation system for efficient removal of Cu(II) complex in water

The efficient remediation of heavy metal complexes in water has become a difficult and challenging task owing to their high stability and strong mobility. In this study, a novel strategy was employed for highly efficient removal of Cu-citrate by using intimately coupled photocatalysis and biodegradation (ICPB) system with non-woven cotton fabric as a carrier. Experimental results showed that the ICPB system caused 94% Cu removal, which was higher than those of single photocatalysis. After 5 cycles, Cu removal efficiency could still reach 78% within 5 h. The existence of 0–40 mg/L citrate had negligible influence, whereas the presence of 60–100 mg/L citrate exhibited a limited adverse effect on Cu removal (∼70%). The decomplexation of Cu-citrate was realized via the function of free radicals and microorganisms. Two main processes, such as bio-adsorption of Cu2+ by microorganisms, deposition of Cu0 on the surface of material, played important role in Cu removal from aqueous solution. The dominant microorganisms in the system were Proteobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Chlorophyta, Planctomycetes, and Verrucomicrobia. Furthermore, the performance of ICPB system was also validated through treatment of other heavy metal complexes. This study provided a feasible strategy for the decontamination of heavy metal complexes in wastewater.