Facile synthesis of bimodal macroporous g-C3N4/SnO2 nanohybrids with enhanced photocatalytic activity

A Robust Pyro-phototronic Route to Markedly Enhanced Photocatalytic Disinfection

Photocatalysis offers a direct, yet robust, approach to eradicate pathogenic bacteria. However, the practical implementation of photocatalytic disinfection faces a significant challenge due to low-efficiency photogenerated carrier separation and transfer. Here, we present an effective approach to improve photocatalytic disinfection performance by exploiting the pyro-phototronic effect through a synergistic combination of pyroelectric properties and photocatalytic processes. A set of comprehensive studies reveals that the temperature fluctuation-induced pyroelectric field promotes photoexcited carrier separation and transfer and thus facilitates the generation of reactive oxygen species and ultimately enhances photocatalytic disinfection performance. It is worth highlighting that the constructed film demonstrated an exceptional antibacterial efficiency exceeding 95% against pathogenic bacteria under temperature fluctuations and light irradiation. Moreover, the versatile modulation role of the pyro-phototronic effect in boosting photocatalytic disinfection was corroborated. This work paves the way for improving photocatalytic disinfection efficiency by harnessing the synergistic potential of various inherent material properties.

Enhanced photocatalytic performance of the N-rGO/g-C3N4 nanocomposite for efficient solar-driven water remediation

This paper describes the synthesis and analysis of a photocatalyst made from a combination of reduced graphene oxide (rGO) and graphitic carbon nitride (g-C3N4) through a simple hydrothermal process. The effectiveness of the N-rGO/g-C3N4 heterostructure in photocatalysis was examined by studying the breakdown of different types of organic pollutants, such as cationic and anionic dyes, as well as antibiotics, under simulated solar light irradiation. Due to the presence of Schottky junctions formed between rGO and g-C3N4, the electron transfer process is significantly enhanced, leading to a reduction in the recombination of photogenerated electrons and holes. As a result, the photocatalytic activity of the rGO/g-C3N4 photocatalyst is significantly higher compared to that of g-C3N4 alone. The photocatalytic performance was further augmented through the nitrogen doping of rGO, which led to an increase in conductivity due to electron doping and an enhancement in the charge separation process. The heterojunction of rGO/g-C3N4 with an optimum concentration of 60% rGO attained a degradation efficiency of 98.7% for rhodamine B (RhB) dye after 50 minutes of light irradiation. In comparison, the nitrogen-doped photocatalyst (N-rGO/g-C3N4) achieved a photodegradation efficiency of 99.99% within 30 minutes. The reaction rate constant of the N-rGO/g-C3N4 nanocomposite was found to be 0.11 min-1 using pseudo first-order rate kinetics. This value is about 16 times more than that of pure g-C3N4 (0.007 min-1) for the degradation of rhodamine B. Additionally, N-rGO/g-C3N4 effectively degraded various contaminants, such as methylene blue, methyl orange, and tetracycline hydrochloride. The paper also addresses the photocatalytic mechanism, which entails the facilitated movement of electrons and holes produced by light, owing to the alignment of energy bands at the interface of the N-rGO/g-C3N4 heterojunction. These findings contribute to the advancement of a metal-free and porous photocatalyst that is highly interconnected and can be used for waste water treatment and environmental remediation.

Self-Assembled Synthesis of Porous Iron-Doped Graphitic Carbon Nitride Nanostructures for Efficient Photocatalytic Hydrogen Evolution and Nitrogen Fixation

In this study, Fe-doped graphitic carbon nitride (Fe-MCNC) with varying Fe contents was synthesized via a supramolecular approach, followed by thermal exfoliation, and was then used for accelerated photocatalytic hydrogen evolution and nitrogen fixation. Various techniques were used to study the physicochemical properties of the MCN (g-C₃N₄ from melamine) and Fe-MCNC (MCN for g-C₃N₄ and C for cyanuric acid) catalysts. The field emission scanning electron microscopy (FE-SEM) images clearly demonstrate that the morphology of Fe-MCNC changes from planar sheets to porous, partially twisted (partially developed nanotube and nanorod) nanostructures. The elemental mapping study confirms the uniform distribution of Fe on the MCNC surface. The X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectroscopy (UV-DRS) results suggest that the Fe species might exist in the Fe³⁺ state and form Fe-N bonds with N atoms, thereby extending the visible light absorption areas and decreasing the band gap of MCN. Furthermore, doping with precise amounts of Fe might induce exfoliation and increase the specific surface area, but excessive Fe could destroy the MCN structure. The optimized Fe-MCNC nanostructure had a specific surface area of 23.6 m² g^-1, which was 8.1 times greater than that of MCN (2.89 m² g^-1). To study its photocatalytic properties, the nanostructure was tested for photocatalytic hydrogen evolution and nitrogen fixation; 2Fe-MCNC shows the highest photocatalytic activity, which is approximately 13.3 times and 2.4 times better, respectively, than MCN-1H. Due to its high efficiency and stability, the Fe-MCNC nanostructure is a promising and ideal photocatalyst for a wide range of applications.

Highly dispersed NiS2 quantum dots as a promising cocatalyst bridged by acetylene black significantly improved the photocatalytic H2 evolution performance of g-C3N4 nanosheets

In this work, ternary nanocomposite (CNs-AB/NiS2) as a novel efficient H2 evolution photocatalyst without the use of noble metals was successfully synthesized by depositing acetylene black (AB) and ultra-fine NiS2 nanoparticles on the surface of CNs (g-C3N4) through ultrasonic dispersion and chemical vapor deposition methods, respectively. It was revealed that the loaded AB and NiS2 nanoparticles have significantly improved the photocatalytic H2 evolution efficiency of the CNs by improving the photogenerated electron-hole pair separation, visible light absorption and hydrogen evolution kinetics. Besides acting as a cocatalyst, AB served as a conductive electron bridge between CNs and NiS2, which accelerated the effective transfer of electrons from CNs to NiS2 and improved the H2 evolution kinetics of the NiS2 cocatalyst. The H2 evolution experiments revealed that the ternary photocatalyst CNs-AB/NiS210 displayed a H2 evolution rate of up to 2434.85 μmoL g-1 h-1, which was a 1.41 times enhancement compared to that of the binary composite CNs-NiS210 and was 12.43 times higher than that of the pure CNs. Moreover, the ternary photocatalyst CNs-AB/NiS210 not only exhibited excellent photocatalytic activity and stability in the tests, but provided a novel idea for the development of high-efficiency catalysts free of noble metals as well.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

Direct complexation of citric acid to synthesize high-efficiency bismuth vanadate through molten polymerization route for the degradation of tetracycline hydrochloride under visible light irradiation

Tetracycline hydrochloride can be efficiently degraded over BiVO4 prepared through direct citric acid complexation.

g-C3N4: Properties, Pore Modifications, and Photocatalytic Applications

Graphitic carbon nitride (g-C3N4), as a polymeric semiconductor, is promising for ecological and economical photocatalytic applications because of its suitable electronic structures, together with the low cost, facile preparation, and metal-free feature. By modifying porous g-C3N4, its photoelectric behaviors could be facilitated with transport channels for photogenerated carriers, reactive substances, and abundant active sites for redox reactions, thus further improving photocatalytic performance. There are three types of methods to modify the pore structure of g-C3N4: hard-template method, soft-template method, and template-free method. Among them, the hard-template method may produce uniform and tunable pores, but requires toxic and environmentally hazardous chemicals to remove the template. In comparison, the soft templates could be removed at high temperatures during the preparation process without any additional steps. However, the soft-template method cannot strictly control the size and morphology of the pores, so prepared samples are not as orderly as the hard-template method. The template-free method does not involve any template, and the pore structure can be formed by designing precursors and exfoliation from bulk g-C3N4 (BCN). Without template support, there was no significant improvement in specific surface area (SSA). In this review, we first demonstrate the impact of pore structure on photoelectric performance. We then discuss pore modification methods, emphasizing comparison of their advantages and disadvantages. Each method's changing trend and development direction is also summarized in combination with the commonly used functional modification methods. Furthermore, we introduce the application prospects of porous g-C3N4 in the subsequent studies. Overall, porous g-C3N4 as an excellent photocatalyst has a huge development space in photocatalysis in the future.

Core@shell structured Au@SnO2 nanoparticles with improved N2 adsorption/activation and electrical conductivity for efficient N2 fixation

The design of electrocatalysts with enhanced adsorption and activation of nitrogen (N₂) is critical for boosting the electrochemical N₂ reduction (ENR). Herein, we developed an efficient strategy to facilitate N₂ adsorption and activation for N₂ electroreduction into ammonia (NH₃) by vacancy engineering of core@shell structured Au@SnO₂ nanoparticles (NPs). We found that the ultrathin amorphous SnO₂ shell with enriched oxygen vacancies was conducive to adsorb N₂ as well as promoted the N₂ activation, meanwhile the metallic Au core ensured the good electrical conductivity for accelerating electrons transport during the electrochemical N₂ reduction reaction, synergistically boosting the N₂ electroreduction catalysis. As confirmed by the ¹⁵N-labeling and controlled experiments, the core@shell Au@amorphous SnO₂ NPs with abundant oxygen vacancies show the best performance for N₂ electroreduction with the NH₃ yield rate of 21.9 μg h^-1 mg^-1_cat and faradaic efficiency of 15.2% at -0.2 V_RHE, which surpass the Au@crystalline SnO₂ NPs, individual Au NPs and all reported Au-based catalysts for ENR.

Improving the photocatalytic hydrogen evolution of UiO-67 by incorporating Ce4+-coordinated bipyridinedicarboxylate ligands

UiO-67 is a Zr-based metal-organic framework (MOF) containing an organic linker namely, the dianion of biphenyl-4,4'-dicarboxylic acid (bpdc). Ce⁴⁺ metal ions (0.02 Ce to Zr atom ratio) were incorporated into UiO-67 via partially replacing bpdc with the dianion of 2,2'-bipyridine-5,5'-dicarboxylic acid (bpydc); thus, the latter forms a bpydc-Ce complex. The resulting product (i.e., UiO-67-Ce) demonstrated a photocatalytic hydrogen evolution rate that was over 10 times higher than that of UiO-67. Through this modification, a new energy transfer channel is opened up. The energy transfer between the bpdc and bpydc-Ce ligands (i.e., from excited bpdc to bpydc-Ce) weakened the recombination of the charge carriers, which was confirmed by photoluminescence, emission lifetime, and transient absorption measurements. This study presents a new way to construct highly efficient MOF photocatalysts.

Constructing highly dispersed 0D Co3S4 quantum dots/2D g-C3N4 nanosheets nanocomposites for excellent photocatalytic performance

The development of noble-metal-free catalysts with high efficiency photocatalytic properties is critical to the heterogeneous catalysis. Herein, zero-dimensional (0D) metal sulfide quantum dots/two-dimensional (2D) g-C₃N₄ nanosheets (Co₃S₄/CNNS) nanocomposites are synthesized by a two-step method, including the ways of in-situ deposition and water bath. The highly dispersed Co₃S₄ quantum dots (particle size is 2-4 nm) are evenly and tightly fixed on CNNS, which can be used as co-catalyst to effectively replace noble metals to improve the photocatalytic properties of CNNS. Co₃S₄/CNNS-900 has the apparent quantum efficiency, which is up to 7.85% at 400 nm. At the same time, the H₂ evolution rate of Co₃S₄/CNNS-900 is 20,536.4 μmol g^-1 h^-1, which is 555 times than CNNS. The excellent photocatalytic performance is due to the highly dispersed Co₃S₄ quantum dots on 2D CNNS, which facilitate the formation of more active sites, Co₃S₄/CNNS promotes the separation and migration of photogenerated carriers, shortens the migration distance of photogenerated carriers, and eventually leads to an increase of the photocatalytic performance.