Flower shaped Bi2O2.33/Bi2WO6 composite: An efficient photocatalyst for degradation of methylene blue from aqueous solution in direct solar light

Herein, we synthesized a Bi2O2.33/Bi2WO6 heterostructure as a platform for the degradation of methylene blue (MB) dye in an aqueous phase. The heterostructure was synthesized by facile ultrasonicated assisted solvothermal method. Various structural, morphological and other techniques such as XRD, FTIR, PL, EIS, UV-DRS, FESEM, HRTEM, XPS, EPR, TGA, BET surface area were used to analyze the characteristics of as-synthesized Bi2O2.33/Bi2WO6. The morphological studies revealed the deposition of Bi2O2.33 flowers in high density on Bi2WO6. Under solar irradiation, 98.6% degradation of MB was achieved in 190 min at optimal conditions (pH = 5, catalyst dose = 0.35 gL-1 and MB concentration = 10 mgL-1). The improved photocatalytic ability of composite in contrast to Bi2O2.33 and Bi2WO6 could be usually ascribed to the interface created between them, assisting the charge transfer. Based on the findings of radical trapping experiments, the charge transfer process over the photocatalyst was completely studied. Additionally, the present heterostructure demonstrated good recyclability over five runs. In nutshell, this study provided a facile approach for synthesizing solar light driven photocatalyst for degradation of methylene blue in aqueous phase and can further explored to be utilized for varied environmental remediation.

Highly Efficient and Reusable PI/TiO2 Organic-Inorganic Microfibers for Sustainable Photocatalytic Degradation of Multiple Organic Pollutants under Simulated Sunlight

Herein, a series of polyimide (PI)/titanium dioxide (TiO2) organic-inorganic flexible composite microfibers with high photocatalytic performance and good reusability were prepared by combining electrospinning technology and a hydrothermal method. Under simulated sunlight, the photocatalytic characteristics of the as-prepared PI nanofibers, TiO2 nanorods, and PI/TiO2 microfibers were evaluated with photocatalytic degradation of Rhodamine B (RhB) solution. Among the tested samples, PI/TiO2-3 mL hydrochloric acid-160 °C-14 h (PI/TiO-3-160-14) (100%) exhibited a superior photocatalytic degradation rate compared to pure PI (84.0%) and TiO2 (62.2%). The enhancement of the photocatalytic performance was attributed to the Z-scheme heterojunction mechanism. When the interface was irradiated by simulated sunlight, the band edge bending, built-in electric field, and Coulomb interaction synergistically facilitated the separation and transport of electron-hole pairs in the heterojunction. This enhanced the oxidation and reduction abilities of the valence and conduction bands of PI/TiO2. These results were adequately verified by X-ray photoelectron spectroscopy (XPS) analyses and radical trapping experiments. Additionally, PI/TiO2 microfibers also demonstrated excellent photocatalytic activity toward methylene blue (MB, 81.4%), methyl orange (MO, 95.9%), and malachite green (KG, 98.9%), underscoring the versatile applicability of PI/TiO2. Further supplementary investigations illustrated that PI/TiO2 microfibers also possess excellent photostability during our extensive recycling photocatalytic experiments.

Band Structure Engineering of Polyimide Photocatalyst for Efficient and Selective Oxidation of Biomass-Derived 5-Hydroxymethylfurfural

Solar-driven high-value utilization of biomass and its derivatives has attracted tremendous attention in replacing fossil sources to generate chemicals. Developing high-performance photocatalysts to selectively catalyze bio-platform molecules remains a challenge. Herein, biomass-based 5-hydroxymethylfurfural (HMF) was efficiently and selectively photooxidized to 2, 5-diformylfuran (DFF) using a metal-free polyimide (PI). PI with moderate photooxidation capacity delivered high DFF selectivity of 91 % and high apparent quantum efficiency of 1.13 %, nearly 7 times higher than that of graphitic carbon nitride. Experimental measurements and theoretical calculations revealed that the band structure and photooxidation capability of PI can be continuously modulated by varying the molar ratio of amine and anhydride. Mechanism analysis depicted that holes and superoxide radicals play crucial roles in the efficient photooxidation of HMF to DFF. This work provides guidance on designing efficient polymeric photocatalysts for oxidating biomass and its derivatives to value-added chemicals.

Graphitic carbon nitride-based photocatalysts in the applications of environmental catalysis

Semiconductor photocatalytic technology has shown great prospects in converting solar energy into chemical energy to mitigate energy crisis and solve environmental pollution problems. The key issue is the development of high-efficiency photocatalysts. Various strategies in the state-of-the-art advancements, such as heterostructure construction, heteroatom doping, metal/single atom loading, and defect engineering, have been presented for the graphitic carbon nitride (g-C₃N₄)-based nanocomposite catalysts to design their surface chemical environments and internal electronic structures to make them more suitable for different photocatalytic applications. In this review, nanoarchitecture design, synthesis methods, photochemical properties, potential photocatalytic applications, and related reaction mechanisms of the modified high-efficiency carbon nitride-based photocatalysts were briefly summarized. The superior photocatalytic performance was identified to be associated with the enhanced visible-light response, fast photoinduced electron-hole separation, efficient charge migration, and increased unsaturated active sites. Moreover, the further advance of the visible-light harvesting and solar-to-energy conversions are proposed.

Deep Eutectic Solvent-Assisted Synthesis of Ternary Heterojunctions for the Oxygen Evolution Reaction and Photocatalysis

Hierarchical nano-/microstructured photocatalysts have drawn attention for enhanced photocatalytic performance. Deep eutectic solvents (DESs) have been used as a green sustainable media to act as both solvent and structure-inducing agent in the synthesis of hierarchical nanomaterials. In this work, the DESs-assisted synthesis of flower-structured BiOCl/BiVO₄ (BOC/BVO) with g-C₃ N₄ (BOC/BVO/g-CN) ternary heterojunctions was achieved by using a simple wet-chemical method, providing good acidic and alkaline oxygen evolution reaction (OER) catalysts. BOC/BVO/g-CN-15 achieved an enhanced photocatalytic activity for OER with an overpotential of 570 mV in 1 m H₂ SO₄ and 220 mV in 1 m KOH electrolyte at a current density of 10 mA cm^-2 with excellent stability and extraordinary durability of the catalyst. The ternary heterojunctions displayed extended lifetimes for photogenerated charges and enhanced the separation efficiency of photogenerated electron-hole pairs, which is helpful to enhance the photocatalytic OER. Furthermore, the photocatalytic performance of the ternary heterojunctions in aqueous solution was demonstrated through photocatalytic dye degradation of methyl orange (MO) as a model pollutant, resulting in 95 % degradation of 20 ppm of MO in 210 min under the irradiation of a 35 W Xe arc lamp. This work not only provides new insight into the design of catalysts by using green solvents but also into the design of highly efficient metal-free OER photocatalysts for applications in acidic and alkaline media.

Highly efficient visible-light-induced photoactivity of carbonized polyimide aerogel for antibiotic degradation

Various nitrogen (N)-doped carbon materials have been designed as efficient photocatalysts. For the first time, polyimide (PI) aerogels were calcined to be N-doped carbon photocatalysts at different temperatures. The structures of the carbonized polyimide aerogels (CPIs) vary with the carbonization temperature. The conductivity of the CPI increases with the improvement of calcination temperature, whereas the N content of the CPI decreases and the N state also changes. Thus, the electronic properties of the CPI are changed. The photocatalytic experiments certified that the PI aerogel calcined at 800 °C exhibited the highest photocatalytic performance. The chlortetracycline (CTC) degradation rate over CPI-800 aerogel is 2.3 times as much as that of PI aerogel due to the changed structure and properties of the CPI-800 aerogel.

Enhancement of photocatalytic hydrogen evolution with catalysts based on carbonized MOF-5 and g-C3N4

The study presents enhancement of photocatalytic hydrogen generation after metal–organic framework (MOF5) carbonization at 700 °C and its utilization as a co-catalyst of graphitic carbon nitride (gCN). Thermal treatment of MOF5 affected the formation of ZnO nanoparticles which played the role of co-catalyst for H₂ evolution. Moreover, significant band-gap narrowing of MOF5 was observed, which also affected the narrowing of the hybrid band gap. The appropriate conduction band position of the carbonized MOF allowed photogenerated electron transfer from gCN to the carbonized MOF, hence, improving the separation of the charge carriers and reducing the overpotential for H₂ generation. The mechanism of the photocatalytic process was also discussed.

The study presents enhancement of photocatalytic hydrogen generation after metal–organic framework (MOF5) carbonization at 700 °C and its utilization as a co-catalyst of graphitic carbon nitride (gCN).

Peroxymonosulfate improved photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composite under visible light irradiation

The photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composites with peroxymonosulfate (PMS) was investigated under visible light irradiation. The photocatalysts were prepared at different activated carbon (AC) loaded percentages and characterized by XRD, FT-IR, BET surface area, SEM, UV-Vis absorbance, photocurrent response and EIS. Several parameters which might influence the degradation efficiency were studied including PMS concentration, solution pH, catalyst dosage, initial atrazine concentration as well as water matrix effect. The results indicated that incorporation of AC contributes effectively in suppressing the recombination of electron-holes pairs and enhancing the photocatalytic performance of graphitic carbon nitride. More significantly, the degradation efficiency of atrazine showed remarkable improvement with PMS addition under visible light irradiation. The reaction rate constant of the 10% AC/g-C₃N₄/Vis/PMS system (0.0376 min^-1) was approximately 2.9 times higher than that of g-C₃N₄/Vis/PMS system (0.0128 min^-1). Results from quenching tests revealed that both sulfate and hydroxyl radicals were involved in the degradation of atrazine, while the latter is the main contributor. This paper constitutes an insight for the metal-free catalyst activation of PMS by photocatalysis for environmental remediation.

Fabrication of a Perylene Tetracarboxylic Diimide-Graphitic Carbon Nitride Heterojunction Photocatalyst for Efficient Degradation of Aqueous Organic Pollutants

Metal-free g-C₃N₄ is a promising candidate for the next-generation visible light-responsive photocatalyst; however, high recombination probability of the photogenerated charge carriers on g-C₃N₄ limits its photocatalytic activity. To further increase the intrinsic photocatalytic activity of g-C₃N₄, here, perylene tetracarboxylic diimide-g-C₃N₄ (PDI/GCN) heterojunctions are prepared by one-step imidization reaction between perylene tetracarboxylic dianhydride (PTCDA) and g-C₃N₄ in aqueous solution. By the combination of various testing results, it is confirmed that the surface hybridization of PTCDA and g-C₃N₄ in the PDI/GCN heterojunctions via O═C-N-C═O covalent bonds occurs at lower PTCDA-to-g-C₃N₄ weight percentage. By selecting p-nitrophenol (PNP) and levofloxacin (LEV) as the target organic pollutants, the visible-light photocatalytic performance of the PDI/GCN heterojunctions is studied. It shows that the PDI/GCN heterojunction prepared at a PTCDA-to-g-C₃N₄ weight percentage of 1% exhibits remarkably higher visible-light photocatalytic degradation and mineralization ability toward aqueous target pollutants as compared with g-C₃N₄ and Degussa P25 TiO₂. On the basis of the experimental results including photoelectrochemistry, indirect chemical probe, and electron spin resonance spectroscopy, it is verified that the surface hybridization in the heterojunctions is responsible for this enhanced photocatalytic activity via accelerating the migration and separation of the photogenerated charge carriers, causing to produce more active species like ^•O₂^-, h_VB⁺, and ^•OH for deep oxidation of PNP or LEV to CO₂ and inorganic anions.

Graphitic-C3N4 quantum dots modified carbon nanotubes as a novel support material for a low Pt loading fuel cell catalyst

A novel graphitic-C₃N₄ quantum dot modified carbon nanotube composite supported PtRu catalyst is prepared by π–π stacking. The enhanced catalytic performance of the catalyst is due to the better dispersion of PtRu NPs and the strong metal–support interaction (SMSI).