Highly efficient and stable p-LaFeO3/n-ZnO heterojunction photocatalyst for phenol degradation under visible light irradiation

Highly Efficient SnIn4S8@ZnO Z-Scheme Heterojunction Photocatalyst for Methylene Blue Photodegradation

Building heterojunctions is a promising strategy for the achievement of highly efficient photocatalysis. Herein, a novel SnIn4S8@ZnO Z-scheme heterostructure with a tight contact interface was successfully constructed using a convenient two-step hydrothermal approach. The phase composition, morphology, specific surface area, as well as photophysical characteristics of SnIn4S8@ZnO were investigated through a series of characterization methods, respectively. Methylene blue (MB) was chosen as the target contaminant for photocatalytic degradation. In addition, the degradation process was fitted with pseudo-first-order kinetics. The as-prepared SnIn4S8@ZnO heterojunctions displayed excellent photocatalytic activities toward MB degradation. The optimized sample (ZS800), in which the molar ratio of ZnO to SnIn4S8 was 800, displayed the highest photodegradation efficiency toward MB (91%) after 20 min. Furthermore, the apparent rate constant of MB photodegradation using ZS800 (0.121 min-1) was 2.2 times that using ZnO (0.054 min-1). The improvement in photocatalytic activity could be ascribed to the efficient spatial separation of photoinduced charge carriers through a Z-scheme heterojunction with an intimate contact interface. The results in this paper bring a novel insight into constructing excellent ZnO-based photocatalytic systems for wastewater purification.

Role of La-based perovskite catalysts in environmental pollution remediation

Since the advent of the industrial revolution, there has been a constant need of efficient catalysts for abatement of industrial toxic pollutants. This phenomenon necessitated the development of eco-friendly, stable, and economically feasible catalytic materials like lanthanum-based perovskite-type oxides (PTOs) having well-defined crystal structure, excellent thermal, and structural stability, exceptional ionic conductivity, redox behavior, and high tunability. In this review, applicability of La-based PTOs in remediation of pollutants, including CO, NO x and VOCs was addressed. A framework for rationalizing reaction mechanism, substitution effect, preparation methods, support, and catalyst shape has been discussed. Furthermore, reactant conversion efficiencies of best PTOs have been compared with noble-metal catalysts for each application. The catalytic properties of the perovskites including electronic and structural properties have been extensively presented. We highlight that a robust understanding of electronic structure of PTOs will help develop perovskite catalysts for other environmental applications involving oxidation or redox reactions.

Enhancing the Photocatalytic Activity of TiO2/Na2Ti6O13 Composites by Gold for the Photodegradation of Phenol

This study aims to synthesize Au/TiO2/Na2Ti6O13 composites to reduce the occurrence of recombination and increase photocatalytic activity in phenol degradation. Gold was used due to its high stability and strong surface plasmon resonance (SPR) properties which make it operate effectively in the visible light spectrum. The prepared composites were characterized using XRD, SEM, TEM, FTIR, and DRS. The results showed that the composite consisted of rutile TiO2 with a crystal size of 38–40 nm and Na2Ti6O13 with a crystal size of 25 nm. The gold in the composite has a crystallite size of 16–19 nm along with the percentage of gold added. Morphological analysis shows that the composite has the form of inhomogeneous spherical particles with gold spread among composites with sizes less than 20 nm. FTIR analysis showed the presence of Na–O and Ti–O–Ti bonds in the composite. The best composite was 3% Au/TiO2/Na2Ti6O13 which had high crystallinity, small particle size, and bandgap energy of 2.59 eV. Furthermore, it had an efficiency 205% better than without gold. After that, cost estimation is proposed as a large-scale application. This study describes the total cost, break-even analysis, and payback analysis for the commercialization needs of the designed photocatalytic catalyst.

Solar heterogeneous photocatalytic degradation of phenol on TiO2/quartz and TiO2/calcite: a statistical and kinetic approach on comparative efficiencies towards a TiO2/glass system

Phenol is a widely used synthetic organic compound, which according to global estimations, is discharged into the environment at a rate of 10 tons/year through industrial waste. Phenol is a recalcitrant pollutant, and human exposure to water containing phenolic substances can lead to health issues. It has been found both in drinking water and wastewater. Solar heterogeneous photocatalytic phenol degradation, measured through chemical oxygen demand, was performed on a thin film tilted plate reactor with TiO₂ immobilized onto different support materials. A full factorial experimental design (4 × 3 × 3) was carried out to statistically evaluate if the independent variables' effects were significant. Four advanced oxidation processes (photolysis, photolysis + H₂O₂, heterogeneous photocatalysis, and heterogeneous photocatalysis + H₂O₂), three support materials (quartz, calcite, and glass), and three pH levels (3, 5.4, and 9) were evaluated. Reaction kinetics were fitted to the pseudo-first-order reaction rate and data was analyzed with an ANCOVA and means test, considering solar light intensity as a covariate. Photolysis/calcite at pH 5.4 and heterogeneous photocatalysis + H₂O₂/glass plate at pH 3 gave the best results, with a reaction rate constant k_ph = 3.047 × 10^-3 min^-1 and k_phC = 4.498 × 10^-3 min^-1, respectively. The three independent variables and their interactions had a significant effect in the phenol degradation (p < 0.05).

Extensive solar light utilizing by ternary C-dots/Cu2O/SrTiO3: Highly enhanced photocatalytic degradation of antibiotics and inactivation of E. coli

Fabrication of a visible-light driven photocatalyst is of great vital for the elimination of antibiotics and microorganism in the wastewater and the construction of sustainable green energy systems. In this work, carbon quantum dots (C-dots) were integrated with Cu₂O/SrTiO₃ p-n heterojunction to optimize the photocatalytic activity. The excellent photocatalytic degradation efficiency of chlortetracycline hydrochloride (CTC·HCl) (92.6% within 90 min) and E. coli inactivation efficiency were observed over C-dots/Cu₂O/SrTiO₃ under visible light irradiation. It is the synergistic effect of p-n heterojunction and modification of C-dots that facilitates the separation and transfer of electron-holes. Meanwhile, the modification of C-dots improves the harvesting of long wavelength solar light of photocatalysts due to its unique up-conversion photoluminescence (UCPL) characteristics. Eventually, the possible photocatalytic degradation path of the catalyst was inferred by LC-MS spectra, and the degradation mechanism was analyzed. This study sheds light on new possibilities for the application of photocatalysts in various light sources and has broad application prospects in water treatment.

Highly efficient piezoelectric field enhanced photocatalytic performance via in situ formation of BaTiO3 on Ti3C2Tx for phenolic compound degradation

Novel BaTiO3/Ti3C2Tx piezo-photocatalysts are fabricated via an in-situ solvothermal method. The synergistic effect of BaTiO3 and Ti3C2Tx increases piezo-photocatalytic activity.

Self-floating photocatalytic hydrogel for efficient removal of Microcystis aeruginosa and degradation of microcystins-LR

Cyanobacterial harmful algal blooms (CyanoHABs) and the release of cyanotoxins have posed adverse impacts to aquatic system and human health. In this study, a novel self-floating Ag/AgCl@LaFeO₃ (ALFO) photocatalytic hydrogel was prepared via freeze-thaw method for removal of Microcystis aeruginosa (M. aeruginosa). The ALFO hydrogel performed an excellent photocatalytic activity with a 99.4% removal efficiency of chlorophyll a within 4 h. It can still remove above 95% chlorophyll a after six consecutive recycles. Besides it has also shown excellent mechanical strength and elasticity, which can ensure its use in practical applications. The mechanisms of M. aeruginosa inactivation are attributed to •O₂^- and •OH generated by the ALFO hydrogel under visible light radiation. In addition, •O₂^- and •OH can further oxidative degrade and even mineralize the leaked algae organic matter, avoiding the recurrence of CyanoHABs. What's more, the ALFO hydrogel owns good photocatalytic degradation performance for microcystins-LR (MC-LR) with a 97% removal efficiency within 90 min. A possible photocatalytic degradation pathway of MC-LR was proposed through the identification of the intermediate products during the photocatalytic reaction, which confirmed the reduction of MC-LR toxicity. This work develops recyclable a self-floating ALFO hydrogel to simultaneously inactivate M. aeruginosa and degrade MC-LR, providing a prospective method for governing and controlling CyanoHABs in practical application.

Recyclable self-floating A-GUN-coated foam as effective visible-light-driven photocatalyst for inactivation of Microcystis aeruginosa

In this work, a recyclable self-floating A-GUN-coated (Ag/AgCl@g-C₃N₄@UIO-66(NH₂)-coated) foam was fabricated for effective inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The floating photocatalyst was able to inactivate 98% of M. aeruginosa within 180 min under the visible-light irrigation, and the floating photocatalyst exhibited a stable performance in various conditions. Moreover, the inactivation efficiency can still maintain nearly 92% after five times recycle experiments, showing excellent photocatalytic stability. Furthermore, effects of A-GUN/SMF floating catalyst on the physiological properties, cellular organics, and algal functional groups of M. aeruginosa were studied. The floating photocatalyst can not only make full use of excellent photocatalytic activities of A-GUN nanocomposite, but also promote contact between catalyst and algae, and realize the effective recovery of the photocatalyst. Finally, possible photocatalytic inactivation mechanisms of algae were obtained, which provides references for removing cyanobacteria blooms in real water bodies.

Efficient integration of plasmonic Ag/AgCl with perovskite-type LaFeO3: Enhanced visible-light photocatalytic activity for removal of harmful algae

A novel plasmonic Ag/AgCl@LaFeO₃ (ALFO) photocatalyst was successfully synthesized by a simple in-situ synthesis method with enhanced photocatalytic activity under visible light for harmful algal blooms (HABs) control. The structure, morphology, chemical states, optical and electrochemical properties of the photocatalyst were systematically investigated using a series of characterization methods. Compared with pure LaFeO₃ and Ag/AgCl, ALFO-20% owned a higher light absorption capacity and lower electron-hole recombined rate. Therefore, ALFO-20% had higher photocatalytic activity with a near 100% removal rate of chlorophyll a within 150 min, whose kinetic constant was 15.36 and 9.61 times faster than those of LaFeO₃ and Ag/AgCl. In addition, the changes of zeta potential, cell membrane permeability, cell morphology, organic matter, total soluble protein, photosynthetic system and antioxidant enzyme system in Microcystis aeruginosa (M. aeruginosa) were studied to explore the mechanism of M. aeruginosa photocatalytic inactivation. The results showed that ALFO-20% could change the permeability and morphology of the algae cell membrane, as well as destroy the photosynthesis system and antioxidant system of M. aeruginosa. What's more, ALFO could further degrade the organic matters flowed out after algae rupture and die, reducing the secondary pollution and avoiding the recurrence of HABs. Finally, the species of reactive oxygen species (ROS) (mainly •O₂^- and •OH) produced by ALFO were determined through quenching experiments, and a possible photocatalytic mechanism was proposed. Overall, ALFO can efficiently remove the harmful algae under the visible light, providing a promising method for controlling HABs.

Enhanced visible-light photocatalysis of clofibric acid using graphitic carbon nitride modified by cerium oxide nanoparticles

Recently, the emerging pharmaceutical micropollutants have become an environmental concern. Herein, we report an efficient elimination of clofibric acid (CA) using visible light-driven g-C₃N₄/CeO₂ prepared by hydrothermal method. Among the catalysts with different compound ratios, g-C₃N₄/CeO₂-3 (1.2 g g-C₃N₄ with 3 mmol Ce(NO₃)₃∙6H₂O) exhibited the best photocatalytic performance. The effect of catalyst dosage was investigated and the optimal value was determined as 0.5 g L^-1. The effect of initial pH (pH₀) showed CA elimination decreased with increasing pH₀. The underlying mechanism for CA oxidation was proposed based on synthetical analysis of photoluminescence emission spectra, transient photocurrent responses, electron paramagnetic resonance, chemical quenching experiments and band edge potential of g-C₃N₄ and CeO₂. Photogenerated hole was primarily responsible for CA elimination while singlet oxygen played an auxiliary role. The products of CA oxidation were detected using liquid chromatography mass spectrometry (LC-MS) method and a possible pathway was put forward. Various organics were used as target contaminants to assess photocatalytic performance of g-C₃N₄/CeO₂ heterojunction under acidic and alkaline pH conditions. The analysis of relationship between the oxidation peak potential (E_OP) and the reaction rate constant indicated that photocatalysis using as prepared g-C₃N₄/CeO₂-3 heterojunction is apt to oxidize contaminants with electron withdrawing group under acid condition.

Visible-light-driven photo-Fenton degradation of ceftriaxone sodium using SnS2/LaFeO3 composite photocatalysts

The LaFeO3-based heterostructure photocatalyst and photo-Fenton process are combined to effectively treat ceftriaxone sodium (CRS) contaminant under visible light.

Enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping Ni2+ and coupling TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation

TOC showing the enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping with Ni2+ and coupling with TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation.

Activity enhancement pathways in LaFeO3@TiO2 heterojunction photocatalysts for visible and solar light driven degradation of myclobutanil pesticide in water

LaFeO₃@TiO₂ heterojunction composites with a core-shell porous structure and LaFeO₃ contents in the 2.5-25 wt.% range have been synthesized via consecutive sol-gel syntheses and tested for the photocatalytic oxidation of the myclobutanil pesticide in water under solar light and pure visible light. Whatever the light spectrum, the kinetic rate constants for both myclobutanil degradation and TOC conversion exhibited a volcano-like profile with increasing the narrow band-gap (2.1 eV) LaFeO₃ content, the optimum composite strongly overperforming both single phases, with full myclobutanil mineralization achieved in 240 min in the best case. The light spectrum influenced the optimum LaFeO₃ content in the composite, being observed at 5 wt.% and 12.5 wt.% under solar and visible light, respectively. This has been attributed to the existence of different light-mediated reaction mechanisms. The optimum LaFeO₃/TiO₂ composite photocatalyst was active and stable after several runs under solar light with leached iron concentration below 0.1 mg/L in solution.

p-n Heterojunction of BiOI/ZnO nanorod arrays for piezo-photocatalytic degradation of bisphenol A in water

p-n Heterojunctions of BiOI/ZnO nanorod arrays (BiOI/ZnO NRs) were prepared by loading the p-type BiOI nanosheets on the n-type ZnO nanorod arrays for efficient removal of organic contaminants in water during the piezo-photocatalytic degradation. Under concurrent visible-light irradiation and ultrasonic vibration, the bisphenol solution (50 mL, 10 mg/L) could be completely degraded within 30 min by 10 mg of 0.15 BiOI/ZnO NRs. It shows a dramatically-enhanced degradation efficiency under light irradiation and ultrasonic vibration, which is four times as high as that only under light irradiation. The excellent piezo-photocatalytic ability of BiOI/ZnO NRs could be attributed to the piezoelectric effect coupling with photocatalytic process. Under the irradiation of light, the electron-hole pairs were generated in BiOI nanosheets, and the piezoelectric potential is created inside the highly oriented one-dimensional ZnO nanorods by ultrasonic vibration, which can accelerate the migration of photogenerated carriers. It shows a strategy to effectively enhance the photocatalytic activity through utilizing the internal piezoelectric potential, which is generated by the one-dimensional nanorods with piezoelectric properties under ultrasonic vibration. So, it can promote the separation and prolong the lifetime of photogenerated carriers, and result in high-efficient degradation of organic contaminants.

Visible-light driven degradation of tetracycline hydrochloride and 2,4-dichlorophenol by film-like N-carbon@N-ZnO catalyst with three-dimensional interconnected nanofibrous structure

The emergence of more and more persistent organic molecules as contaminants in water simulates research towards the development of more advanced technologies, among which photocatalysis is a feasible choice. However, it is still challenging to design a photocatalyst that fulfills all the requirements for industrial application, i.e., active under visible-light irradiation, shape with handy convenience, highly uniform distribution of active sites, substrate with excellent electronic properties, etc. In this study, we report an attempt to solve these issues at once by designing a film-like photocatalyst with uniform distribution of nitrogen-doped ZnO nanoparticles along nitrogen-doped carbon ultrafine nanofibers with three-dimensional interconnected structure. Under visible-light irradiation, the product exhibited remarkable reactivity for the degradation of two model pollutants tetracycline hydrochloride and 2,4-dichlorophenol within 100 min. The cyclic experiments demonstrated only a slight loss (ca. 5 %) of reactivity after five consecutive photocatalytic reactions. We also investigated the detailed relationship between the structural features and the superior properties of this product, as well as the degradation mechanisms. The convenient shape of the product with excellent performances for the treatment of real polluted water increases its suitability for larger scale application. Our work provides a rational design of photocatalysts for environmental remediation.

Bio-photoelectrochemcial system constructed with BiVO4/RGO photocathode for 2,4-dichlorophenol degradation: BiVO4/RGO optimization, degradation performance and mechanism

A single-chamber bio-photoelectrochemical system (BPES) constructed with BiVO₄/reduced graphene oxide (RGO) photocathode was proposed for 2,4-dichlorophenol (2,4-DCP) degradation under simulated solar irradiation. The BiVO₄/RGO (B/G) composites were synthesized, optimized and characterized by various techniques to analyze their physico-chemical and photocatalytic properties. Results showed that B/G (5 wt% - 9 h - 150 °C) exhibited the best photocatalytic activity for 2,4-DCP degradation, which was 1.5 times of that of BiVO₄, due to its better light absorption, faster electrons transfer, and more efficient photo-generated e^- - h⁺ separation. Reactive species trapping experiments revealed that ·OH was the main radical leading to 2,4-DCP degradation, and h⁺ also influenced 2,4-DCP removal. The 2,4-DCP (20 mg/L) removal rate and current output from the illuminated BPES were much higher than those of the unilluminated reactor (68.5 % vs. 41.8 %, 60.31 A/m³ vs. 40.07 A/m³) in 24 h, and the cathode potential was more negative, indicating that photocathode catalytic process was favorable to pollutants degradation and energy generation. Intermediates of 2,4-DCP degradation in the BPES were identified, and accordingly, possible degradation pathway and mechanism were proposed. This research advanced the development of efficient photocathode and mechanism of recalcitrant wastewater treatment in the BPES.

Construction of TiO2/Ag3PO4 nanojunctions on carbon fiber cloth for photocatalytically removing various organic pollutants in static or flowing wastewater

Plenty of power-shaped semiconductor nanomaterials have been used to photocatalytically degrade various pollutant wastewater in beakers, but they are difficult to be applied in the practical wastewater that is flowing in river or pipeline. Thus, the key to photocatalytically degrading the flowing wastewater is to develop flexible large-scale filter-membrane with high photocatalytic activity. To address the issue, with carbon fiber cloth (CFC) as the porous substrate and TiO₂/Ag₃PO₄ as ultraviolet/visible (UV/Vis) responsed components, we reported the in-situ growth of TiO₂/Ag₃PO₄ nanojunctions on CFC as filter-membrane-shaped photocatalyst. The resulting CFC/TiO₂/Ag₃PO₄ is composed of CFC whose surface is decorated with TiO₂ nanorods (length: 1 ± 0.5 μm, diameter: 150 ± 50 nm) and Ag₃PO₄ nanoparticles (diameter: 20-100 nm). CFC/TiO₂/Ag₃PO₄ displays a broad absorption region with two edges (~410 and ~510 nm), owing to the bandgaps of TiO₂ and Ag₃PO₄. Under Vis or UV-Vis light illumination, CFC/TiO₂/Ag₃PO₄ (4 × 4 cm²) can efficiently degrade more phenol (80.6%/89.4%), tetracycline (TC, 91.7%/94.2%), rhodamine B (RhB, 98.4%/99.5%) and acid orange 7 (AO7, 97.6%/98.3%) in the beaker than CFC/TiO₂ or CFC/Ag₃PO₄. Especially, CFC/TiO₂/Ag₃PO₄ (diameter: ~10 cm) as the filter-membrane was used to construct multiple device for degrading the flowing RhB wastewater. The removal efficiency of RhB increases from 19.6% at the 1st pool to 96.8% at the 8th pool. Therefore, this study brings some insights for purifying organic pollutants in static or flowing wastewater by using filter-membrane-shaped photocatalysts.