Hou Wang

Highly efficient visible-light-induced photoactivity of Z-scheme Ag2CO3/Ag/WO3 photocatalysts for organic pollutant degradation

Novel and efficient Z-scheme Ag2CO3/Ag/WO3 with excellent visible-light-driven photocatalytic performance was fabricated using a facile deposition and photochemical reduction process. Surface, morphological, and structural properties of the resulting materials were characterized using N2 sorption–desorption and Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis and photoluminescence spectroscopy. The photocatalytic performances of the Ag2CO3/Ag/WO3 composites were evaluated by the degradation of rhodamine B (RhB), methyl orange (MO), ciprofloxacin (CIP), and tetracycline hydrochloride (TC) under visible light irradiation. The results demonstrate that the novel Z-scheme Ag2CO3/Ag/WO3 composites exhibit higher photocatalytic activity than pure Ag2CO3 rods and WO3 nanoparticles. The enhanced photocatalytic activity of Ag2CO3/Ag/WO3 can be ascribed to the extended absorption in the visible light region caused by a surface plasmon resonance (SPR) effect, effective separation of photogenerated charges, and the formation of a Z-scheme system. In addition, the photocatalyst exhibits high stability and reusability. This work could offer a new insight into the design and fabrication of advanced materials with Z-scheme structures for photocatalytic applications for organic pollutants removal from wastewater.

Functionality of surfactants in waste-activated sludge treatment: A review

Proper treatment of waste-activated sludge (WAS) involves three pivotal processes, dewatering, anaerobic digestion, and pollutants removal, which need to be re-assessed urgently. Although many traditional sludge treatments have been developed, it is prudent to enhance the efficiency of sludge treatment using multifunctional, flexible, and environmentally friendly surfactants. With regard to sludge dewatering, surfactants can weaken the binding interaction between sludge flocs and promote the dissolution of extracellular polymeric substances (EPSs), resulting in the release of bound water. Using surfactants in anaerobic digestion promotes the release of enzymes trapped in sludge and improves the activity of enzymes during hydrolysis. Owing to their characteristic encapsulation of hydrophobes into self-assembled aggregates (micelles), surfactants can form host-guest complexes with polycyclic aromatic hydrocarbons (PAHs). Additionally, surfactants can enhance the desorption of heavy metals and prevent the emergence of heavy metal residue. This review summarizes the current surfactant-based sludge treatment technologies according to their roles in sludge disposal solutions. Then, possible mechanisms of surfactants in sludge dewatering, anaerobic digestion, and the removal of organic pollutants and heavy metals are analysed systemically. Finally, changes to sludge treatment via the aid of surfactants are highlighted. This review presents the comprehensive advances in the use of surfactants in WAS reduction, recycling, and risk relief, underscoring their roles in increasing economic efficiency and ensuring environmental quality.

Construction of an all-solid-state Z-scheme photocatalyst based on graphite carbon nitride and its enhancement to catalytic activity

Photocatalysis is a promising technology that can contribute to energy conversion and environmental remediation. Nowadays, the major focus in photocatalysis is the fabrication and development of photocatalytic materials. Graphitic carbon nitride (g-C3N4) has attracted intensive attention because of its low cost, facile preparation, high chemical stability, and non-toxicity. However, it is difficult for pristine g-C3N4 to simultaneously have wide absorption range, high stability, efficient charge separation and strong redox ability, which limits its practical applications. In this review, an artificial g-C3N4-based Z-scheme photocatalyst that simulates natural photosynthesis is presented and thoroughly discussed in terms of the design, preparation, and applications. In particular, the all-solid-state g-C3N4-based Z-scheme system, without reversible redox mediators, has been extensively applied in water splitting, CO2 conversion, and pollutant degradation. Typically, metal oxides, metal sulfides, bismuth-based photocatalytic semiconductors and silver-based photocatalytic semiconductors have been explored for the design of Z-scheme systems with g-C3N4 to enhance the photocatalytic activity by widening the light absorption, facilitating the charge separation, promoting the redox ability and prolonging the charge carrier lifetime. The challenges and prospects for the design and application of g-C3N4-based Z-scheme photocatalysts are also proposed.

Nitrogen doped carbon quantum dots mediated silver phosphate/bismuth vanadate Z-scheme photocatalyst for enhanced antibiotic degradation

A novel nitrogen doped carbon quantum dots (N-CQDs) mediated Ag3PO4/BiVO4 Z-scheme photocatalyst was synthesized through a solvothermal-precipitation method. The as-prepared photocatalysts were comprehensive characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, transmission electron micrograph, UV-vis diffuse reflection spectroscopy, vis photoluminescence and electron spin resonance analysis. The photocatalytic performances of as-prepared photocatalysts were used for degradation of tetracycline (TC) under visible-light illumination. Results exhibited the increased photocatalytic efficiency of BiVO4/N-CQDs/Ag3PO4-10 (Ag3PO4 with the mass ratio of BiVO4/N-CQDs/Ag3PO4u202f=u202f10%) to photodegrade TC is up to 88.9% in 30u202fmin and 59.8% mineralization in 90u202fmin. The degradation reaction coefficient (k) is about 6.00, 2.78 and 1.80 times higher than that of BiVO4, N-CQDs/BiVO4 and Ag3PO4/BiVO4, respectively. The excellent photocatalytic performance of the Z-scheme BiVO4/N-CQDs/Ag3PO4 was attributed to the construction of Z-scheme system, increased light harvesting capacity and improved molecular oxygen activation ability. Moreover, the photocatalytic activity of BiVO4/N-CQDs/Ag3PO4 remained 79.9% after five cycling runs, indicating the high stability and reusability of the as-prepared photocatalyst. Additionally, a possible photocatalytic mechanism of the novel Z-scheme BiVO4/N-CQDs/Ag3PO4 was proposed.

Visible-light-driven removal of tetracycline antibiotics and reclamation of hydrogen energy from natural water matrices and wastewater by polymeric carbon nitride foam

Water and energy are key sustainability issues that need to be addressed. Photocatalysis represents an attractive means to not only remediate polluted waters, but also harness solar energy. Unfortunately, the employment of photocatalysts remains a practical challenge in terms of high cost, low efficiency, secondary pollution and unexploited water matrices influence. This study investigated the feasibility of photocatalysis to both treat water and produce hydrogen with practical water systems. Polymeric carbon nitride foam (CNF) with large surface area and mesoporous structure was successfully prepared via the bubble-template effect of ammonium chloride decomposition during thermal condensation. The reaction kinetics, mechanisms, and effect of natural water matrices and wastewater on CNF-based photocatalytic removal of tetracycline hydrochloride (TC-HCl) were systematically investigated. Furthermore, the efficiency of clean hydrogen energy from natural water matrices and wastewater was also evaluated. It was found that the photocatalytic performance of CNF for TC-HCl removal was principally affected by calcination temperature in the presence of NH4Cl. The degradation rates of CNF-4 (calcined at 550u202f°C) were approximately 1.84, 2.49 and 7.47 times than that of the CNF-2 (calcined at 600u202f°C), CNF-1 (calcined at 500u202f°C) and GCN (without NH4Cl), respectively. Results indicate that the improved photocatalytic performance was predominantly ascribed to the large specific surface area, increased availability of exposed active sites, and enhanced transport and separation efficiency of the photogenerated carrier. Based on electron spin resonance, chemical trapping experiment and density functional theory calculation, photoinduced oxidizing species (·O2- and holes) initially attacked the C-N-C fragment of TC molecules, which were finally mineralized to CO2, water and inorganic matters. Under the synergistic influence of water constituents (including acidity and alkalinity, ion species and dissolved organic substances), various water matrices greatly affected the degradation rate of TC-HCl, with the highest removal efficiency of 78.9% in natural seawater, followed by reservoir water (75.0%), tap water (62.3%), deionized water (49.8%), reverse osmosis concentrate (32.7%) and pharmaceutical wastewater (18.9%). Interestingly, low amounts of the emerging microplastics slightly improved TC-HCl removal, whereas high amounts (1.428u202f×u202f107u202fP/cm3) restricted removal due to light absorption and the intrinsic adsorption interaction. Moreover, the photocatalysts were able over repeated usage. Notably, the hydrogen yields rates of polymeric carbon nitride foam were 352.2, 299.8, 184.9 and 94.3u202fμmol/g/h in natural seawater, pharmaceutical wastewater, water from reservoir and tap water, respectively. This study proves the potential of novel nonmetal porous photocatalyst to simultaneously treat wastewater while converting solar energy into clean hydrogen energy.