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The construction of highly efficient and multifunctional composite photocatalysts has attracted extensive attention in the field of environmental governance. In this study, an efficient coated ZH-scheme (SnS2@CdS)/TiO2(0 0 1) photocatalyst is resoundingly prepared by hydrothermal, isoelectric point and continuous ion layer adsorption reaction methods and a sequence of characterizations are carried out. The photocatalytic activity of (SnS2@CdS)/TiO2(0 0 1) photocatalyst is evaluated via degradation of phenol with simultaneous conversion of Cr(VI) under sunlight irradiation. Furthermore, the effects of initial concentrations of phenol and Cr(VI), variety of photocatalyst, solution pH, (SnS2@CdS)/TiO2(0 0 1) photocatalyst dosage and recycling times on phenol degradation and Cr(VI) conversion are investigated. The crucial active species of phenol degradation are explored by capture experiments. When the coated ZH-scheme (SnS2@CdS)/TiO2(0 0 1) photocatalyst dosage is 1.0 g/L, phenol and Cr(VI) concentrations are 20 mg/L and 40 mg/L, respectively and solution pH is 4.0, the phenol degradation rate and the Cr(VI) conversion rate could reach 85.52 % and 95.69 %, respectively. Additionally, the possible photocatalytic mechanism of phenol degradation with synchronous Cr(VI) conversion caused by (SnS2@CdS)/TiO2(0 0 1) photocatalyst is proposed. It can be hoped that this work will provide a feasible way to treat high concentrations of organic pollutants and simultaneously convert heavy metal ions.

To better understand the inception direction and breakdown characteristics of negative sparks in rod–rod air gaps, experiments have been carried out with negative 250/2500μs voltage impulses in 0.4m-1.2m air gaps. Three types of air gaps were used including rod-double rods air gaps and two kinds of rod–rod air gaps. Initial angle of spark channel defined as the angle between tangential directions of the initial spark channel to vertical was found to follow Normal distribution in rod–rod air gaps. The average initial angle of negative sparks in rod–rod air gaps is 14°-62° which is larger than that of positive sparks in 0.5m rod-plane air gaps and close to those in 7m-8m rod-plane air gaps. The inception direction and breakdown characteristics of 0.4m-1.2m rod–rod air gaps are influenced by gap distance, grounded rod tip shape and applied voltage amplitude. The negative 50% breakdown voltage increases linearly with gap distance, which is also influenced by gap configuration. As gap distance was elongated, longer upward streamer occurred at conical grounded rod tip resulting in larger attraction and higher striking probability of grounded rod with conical tip; with higher voltage amplitude, the initial angle and striking selectivity of grounded rods become more random.

Photocatalysis technology is an effective way for converting nitrate (NO3−) and sulfite (SO32−) in wastewater to pollution-free nitrogen (N2) and exploitable ammonium sulfate ((NH4)2SO4). In this study, three novel photocatalysts, Z-scheme (Cu,Cu)/g–C3N4–(Cu,Cu)-WO3(002), Z-scheme (Cu,Ag)/g–C3N4–(Cu,Ag)-WO3(002) and Z-scheme (Cu,Ru)/g–C3N4–(Cu,Ru)-WO3(002), were prepared by photo-assisted electrostatic self-assembly method. The prepared photocatalysts are synthetically characterized by XRD, SEM, TEM, EDX, XPS, DRS, PL, TPR and EIS. The effects of different co-catalyst combinations on the activity and selectivity of the photocatalysts are evaluated. Also, the impacts of simulated solar light irradiation time, NO3− initial concentration and cycle times on the conversions of NO3− and SO32− are studied. The results display that the Z-scheme (Cu,Ag)/g–C3N4–(Cu,Ag)-WO3(002) photocatalyst can selectively convert NO3− to N2, while the Z-scheme (Cu,Ru)/g–C3N4–(Cu,Ru)-WO3(002) photocatalyst can selectively convert NO3− to NH4+. Nevertheless, the Z-scheme (Cu,Cu)/g–C3N4–(Cu,Cu)-WO3(002) photocatalyst has hardly selectivity for conversion of NO3−. These three photocatalysts all exhibit relatively strong capabilities for converting SO32− to sulfate (SO42−) due to the existence of the highly active (002) plane of WO3. Finally, the possible mechanisms on the photocatalytic conversions of NO3− and SO32− caused by Z-scheme (Cu,M)/g–C3N4–(Cu,M)-WO3(002) (M = Cu, Ag and Ru) photocatalysts are proposed.

Designing efficient photocatalyst for degradation and conversion of nitrogenous organic pollutants is meaningful to remediate the water environment. In this research, a dual Z-scheme Bi2MoO6/Bi2WO6\AgI\Ag photocatalyst is prepared via isoelectric point and continuous ion layer adsorption methods. The morphology, structure, composition and photoelectrical property of the acquired photocatalyst are investigated by multiple characterization techniques. The activity of the prepared photocatalyst is evaluated by degrading malachite green (MG) and converting the generated nitrate (NO3−) and nitrite (NO2−) ions into nitrogen (N2). The results reveal that the Z-scheme Bi2MoO6/Bi2WO6\AgI\Ag photocatalyst possesses high degradation ratio of MG and generation ratio of N2 under solar light irradiating for 180 min at pH = 5.0. It can be attributed to the fabrication of dual Z-scheme Bi2MoO6/Bi2WO6\AgI photocatalytic system and the deposition of Ag nanoparticle as co-catalyst, which enables the photocatalyst to have high separation efficiency of electrons and holes and strong selectivity for the conversions of NO3− and NO2− into N2. The cycle experiment and XRD test confirm the preeminent stability and reusability of the photocatalyst. The trapping and electron spin resonance (ESR) experiments verify that the hole plays a vital part in the degradation of MG, electron and carbon dioxide free radicals (•CO2−) are in charge of the conversions of NO3− and NO2− ions. Furthermore, a probable mechanism on degradation of the nitrogenous organic pollutants and conversions of the generated NO3− and NO2− ions induced by Z-scheme Bi2MoO6/Bi2WO6\AgI\Ag photocatalyst is put forward.

A high-efficiency Z-scheme photocatalyst, Er3+:YAlO3@(Au/SrTiO3)-Au-WO3, is fabricated successfully via hydrothermal and photo-deposition methods. All as-prepared samples are characterized by XRD, SEM, TEM, FT-IR, EDX, XPS, Raman spectroscopy, PL and DRS. The activity of the prepared Z-scheme Er3+:YAlO3@(Au/SrTiO3)-Au-WO3 photocatalyst is evaluated through photocatalytic conversion of Cr(VI) under simulated solar light irradiation. The meaningful influencing factors such as simulated solar light irradiation time, light intensity, sacrificial agents and cycling times are investigated. The results displayed that the existence of Er3+:YAlO3 can improve the utilization ratio of solar light for wide band-gap SrTiO3. Moreover, the formation of Z-scheme SrTiO3/WO3 photocatalytic system and the introduction of Au nanoparticles as electron mediator and co-catalyst can promote the separation of photo-induced electron and hole to obtain much high photocatalytic activity. Finally, the mechanism on conversion of Cr(VI) caused by Z-scheme Er3+:YAlO3@(Au/SrTiO3)-Au-WO3 photocatalyst is put forward. © 2021 Elsevier B.V. All rights reserved.

Several novel Z-scheme CuPd/SrTiO3–CuPd–Bi2O3 photocatalysts are prepared via chemical reduction and calcination methods to degrade organic dyes containing N and S and convert NO2-, NO3- and SO32- into (NH4)2SO4. Sodium borohydride (NaBH4), ascorbic acid (C6H8O6) and hydrazine hydrate (N2H4·H2O) are selected as reductants to deposit CuPd alloy nanoparticles on corresponding photocatalyst. The influence of solar light irradiation time on photocatalytic degradation of organic dye and conversion of the generated inorganic ions is studied. The reusability and stability of the prepared photocatalysts are assessed. The results indicate that the Z-scheme CuPd/SrTiO3–CuPd–Bi2O3 photocatalyst prepared by using NaBH4 has best photocatalytic activity, reusability and stability. The capture experiment of active species proves that holes play crucial roles in photocatalytic degradation of organic dyes and conversion of SO32- and electrons are momentous for the conversions of NO2- and NO3-. A possible mechanism on photocatalytic degradation of organic dyes containing N and S and conversions of NO2-, NO3- and SO32- into (NH4)2SO4 caused by Z-scheme CuPd/SrTiO3–CuPd–Bi2O3 photocatalyst is proposed.

A novel Z-scheme WO3:Yb3+,Er3+/Ag/Ag3VO4/Ag photocatalyst is prepared via hydrothermal and calcination methods. In this system, WO3:Yb3+,Er3+ is used as an excellent up-conversion luminescent agent and highly active photocatalyst to broaden the light response range. Ag with SPR effect is regarded as electronic channel and cocatalyst to accelerate electron transfer and increase hydrogen production. The photocatalytic performance of Z-scheme WO3:Yb3+,Er3+/Ag/Ag3VO4/Ag photocatalyst is assessed by levofloxacin degradation with synchronous hydrogen production. Some influence factors, sunlight irradiation time, sacrificial agent concentration and catalyst cycle number, are discussed. The emission light spectrum and energy conversion mechanism of WO3:Yb3+,Er3+ are studied. The photocatalyst gives prominent degradation ratio (90.44 %) and hydrogen production amount (489.02 μmol/g) under sunlight irradiation for 180 min. It shows a high stability and reusability in levofloxacin degradation with synchronous hydrogen production within five cycles. The possible mechanism of levofloxacin degradation with synchronous hydrogen production caused by Z-scheme WO3:Yb3+,Er3+/Ag/Ag3VO4/Ag photocatalyst is proposed.