Preparation of sponge carrier supported photocatalyst by self-assembly technique for phenol photodegradation in visible light

Insight into integration of photocatalytic and microbial wastewater treatment technologies for recalcitrant organic pollutants: From sequential to simultaneous reactions

The more and more stringent environmental standards for recalcitrant organic pollutants pushed forward the development of integration of photocatalytic and microbial wastewater treatment technologies. The past studies proposed mainly two typical integration ways: a) Independent sequence of photocatalysis and biodegradation (ISPB) conducting the sequential reactions; b) Intimate coupling of photocatalysis and biodegradation (ICPB) conducting the simultaneous reactions. Although ICPB has received more attraction recently due to its novelty, ISPB gives an edge in certain cases. The article reviews the state-of-the-art ISPB and ICPB studies to comprehensively compare the two systems. The strengths and weaknesses of ISPB and ICPB regarding the treatment efficiency, cost, toxicity endurance and flexibility are contradistinguished. The reactor set-ups, photocatalysts, microbial characteristics of ISPB and ICPB are summarized. The applications for different kinds of recalcitrant compounds are elaborated to give a holistic view of the removal efficiencies and transformation pathways by the two technologies. Currently, in-depth understandings about the interference among mixed pollutants, co-existing components and key parameters in realistic wastewater are urgently needed. The long-term and large-scale application cases of the integration technologies are still rare. Overall, we conclude that both ISPB and ICPB technologies are reaching maturity while challenges still exist for two systems especially regarding the reliability, economy and generalization for realistic wastewater treatment plants. Future research should not only manage to reduce the cost and energy consumption by upgrading reactors and developing novel catalysts, but also attach importance to the cocktail effects of wastewater during the sequential or simultaneous photocatalysis and biodegradation.

Non-Stacked γ-Fe2O3/C@TiO2 Double-Layer Hollow Nanoparticles for Enhanced Photocatalytic Applications under Visible Light

Herein, a non-stacked γ-Fe₂O₃/C@TiO₂ double-layer hollow nano photocatalyst has been developed with ultrathin nanosheets-assembled double shells for photodegradation phenol. High catalytic performance was found that the phenol could be completely degraded in 135 min under visible light, due to the moderate band edge position (VB at 0.59 eV and CB at −0.66 eV) of the non-stacked γ-Fe₂O₃/C@TiO₂, which can expand the excitation wavelength range into the visible light region and produce a high concentration of free radicals (such as ·OH, ·O²⁻, holes). Furthermore, the interior of the hollow composite γ-Fe₂O₃ is responsible for charge generation, and the carbon matrix facilitates charge transfer to the external TiO₂ shell. This overlap improved the selection/utilization efficiency, while the unique non-stacked double-layered structure inhibited initial charge recombination over the photocatalysts. This work provides new approaches for photocatalytic applications with γ-Fe₂O₃/C-based materials.

Intimate coupling of photocatalysis and biodegradation for wastewater treatment: Mechanisms, recent advances and environmental applications

Due to the increase of emerging contaminants in water, how to use new treatment technology to make up for the defects of traditional wastewater treatment method has become one of the research hotspots at present. Intimate coupling of photocatalysis and biodegradation (ICPB) as a novel wastewater treatment method, which combines the advantages of biological treatment and photocatalytic reactions, has shown a great potential as a low-cost, environmental friendly and sustainable treatment technology. The system mainly consists of photocatalytic materials, porous carriers and biofilm. The key principle of ICPB is to transform bio-recalcitrant pollutants into biodegradable products by photocatalysis on the surface of porous carriers. The biodegradable products were mineralized simultaneously through the biofilm inside the carriers. Because of the protection of the carriers, the microorganism can remain active even under the UV-light, the mechanical force of water flow or the attack of free radicals. ICPB breaks the traditional concept that photocatalytic reaction and biodegradation must be separated in different reactors, improves the purification capacity of sewage and saves the cost. This review summarizes the recent advances of ICPB photocatalysts, carriers and biofilm being applied, and focuses on the mechanisms and reactor configurations which is particularly novel. Furthermore, the possible ongoing researches on ICPB are also put forward. This review will provide a valuable insight into the design and application of ICPB in environment and energy field.

Respective construction of Type-II and direct Z-scheme heterostructure by selectively depositing CdS on {001} and {101} facets of TiO2 nanosheet with CDots modification: A comprehensive comparison

Directional deposition has always been a focus issue in the construction of specific heterostructure. Herein, for the first time, we have demonstrated that the CdS could be selectively deposited on {001} or {101} facets of TiO₂ nanosheet, and two different charge transfer processes were formed. First, the selective deposition of CdS on {001} facets of TiO₂ nanosheet ({001}TiO₂/CdS) would form the Type-II heterostructure, which seriously weakened the redox ability of {001}TiO₂/CdS and directly resulted in the low photocatalytic performance (4-Chlorophenol (4-CP), 61.92% in 40 min) and serious photocorrosion of CdS. In contrary, the selective deposition of CdS on {101} facets of TiO₂ nanosheet ({101}TiO₂/CdS) could construct direct Z-scheme heterostructure with significantly increased photocatalytic 4-CP degradation efficiency (96.12%), much higher than pristine TiO₂ nanosheet (87.21%). The hybrids were further modified by carbon nanodots (CDots) ({101}TiO₂/CdS/CDots) to enhance photocatalytic performance (99.84%). The obtained direct Z-scheme {101}TiO₂/CdS/CDots showed excellent stability and anti-photocorrosion ability. The synergistic effect between TiO₂ nanosheet, CdS and CDots was expounded through characterization analyses, and the photocatalytic reaction mechanism was proposed in detail. Toxicity assessment authenticated good biocompatibility and low cytotoxicity of {101}TiO₂/CdS/CDots. Our discovery was expected to drive great advances in the use of TiO₂ nanosheet for environmental remediation.