Crystalline heptazine carbon nitride (HCN) is an ideal photocatalyst for photocatalytic ammonia synthesis. However, the limited response to visible light has hindered its further development. As a noble metal, Au nanoparticles (NPs) can enhance the light absorption capability of photocatalysts by the surface plasmon resonance (SPR) effect. Therefore, a series of Au NPs-loaded crystalline carbon nitride materials (AH) were prepared for photocatalytic nitrogen fixation. The results showed that the AH displayed significantly improved light absorption and decreased recombination rate of photo-generated carriers owing to the introduction of Au NPs. The optimal 2AH (loaded with 2 wt% Au) sample demonstrated the best photocatalytic performance for ammonia production with a yield of 70.3 μmol g− 1 h− 1, which outperformed that of HCN. This can be attributed to the SPR effect of Au NPs and alkali metal of HCN structure. These findings provide a theoretical basis for studying noble metal-enhanced photocatalytic activity for nitrogen fixation and offer new insights into advances in efficient photocatalysts.

This study examines the effects of the TiO2 content and TiO2 position in the core or shell within tubular carbon nanofibers on the photocatalytic activity under visible light. Core–shell tubular carbon nanofiber composites whose cores are filled with TiO2 nanoparticles (PMTi(10)P) are fabricated through coaxial electrospinning and subsequent heat treatment. The PMTi(10)P composites with well-preserved TiO2 nanoparticles in the core part induce more oxygen vacancies, Ti3+ species, chemisorbed oxygen species, and anatase phases, significantly improving the photocatalytic performance. They act as photoelectron traps, allowing more photoelectrons and holes to participate in the photocatalytic reaction and extending the absorbance of TiO2 to the visible light region. The resulting PMTi(10)P photocatalyst exhibits excellent performance of 100% removal of methylene blue within 30 min and maintains nearly 100% removal of 15 ppm methylene blue over 10 regeneration cycles, indicating consistent and stable photocatalytic performance.

With the development of photocatalytic hydrogen production technology, the effective transport of photogenerated carrier electrons is still one of the main factors affecting the performance of photocatalytic hydrogen evolution. In this work, graphdiyne was prepared by ball milling method. The CoMo-MOF with polyhedral structure was introduced into graphdiyne to construct S-scheme heterojunction to promote the efficient transfer of photogenerated carriers and enhanced hydrogen evolution activity. Graphdiyne is a new carbon material with adjustable band gap, which is synthesized from the hybrid of sp and sp2, and has excellent electrical conductivity. CoMo-MOF is a polyhedral structure that can provide more active sites and promote photocatalytic hydrogen evolution. The weak point of poor conductivity in CoMo-MOF has been successfully improved by combining CoMo-MOF with graphdiyne, and the migration rate of photogenerated carriers has been accelerated. The hydrogen evolution property of graphdiyne/CoMo-MOF is 300 μmol, which is 19.61 times that of graphdiyne and 9.03 times that of CoMo-MOF. Therefore, the construction of S-scheme heterojunction provides a transport channel for electron transfer and improves the efficiency of photogenerated carrier separation. This work provides a new train of thought of design to introduce MOFs materials into carbon materials for photocatalytic hydrogen evolution.

Building step-scheme (S-scheme) heterojunctions has recently emerged as a highly effective approach for developing superior photocatalysts for water purification. Herein, a C3N5/ Ag3PO4 (CA) S-scheme heterojunction was prepared by in situ growth of Ag3PO4 nanoparticles on 2D C3N5 nanosheets. Notably, under visible-light irridiation, CA exhibited significantly higher activity in the photodegradation of LEVO, which is about 28.38, 2.41, and 2.14 times higher than the rates for C3N5, Ag3PO4, and the mixture, respectively. Based on the radical scavenging experiments, the mechanism for enhanced photocatalytic performance has been analyzed, is attributed to improved interfacial charge separation, the elevated redox potential of photon-generated electrons and holes, and the increased generation of active species resulting from the S-scheme transfer of photoinduced carriers. Additionally, CA demonstrates greater stability than either C3N5 or Ag3PO4 alone in the photo-oxidation of LEVO and the photodegradation of RhB. In essence, this study not only deepens our comprehension of the photocatalytic mechanism of CA, but also pioneers a novel concept for the development of highly effective and stable S-type heterojunction photocatalysts.

Photocatalytically splitting water into hydrogen upon semiconductors has tremendous potential for alleviating environmental and energy crisis issues. There is increasing attention on improving solar light utilization and engineering photogenerated charge transfer of TiO2 photocatalyst because it has advantages of low cost, non-toxicity, and high chemical stability. Herein, oxygen vacancies and cocatalysts (Cu and MoS2) were simultaneously introduced into TiO2 nanoparticles from protonic titanate by a one-pot solvothermal method. The composition and structure characterization confirmed that the pristine TiO2 nanoparticle was rich in oxygen vacancies. The photocatalytic performances of the composites were evaluated by solar-tohydrogen evolution test. The results revealed that both Cu-TiO2 and MoS2- TiO2 could improve the photocatalytic hydrogen evolution ability. Among them, 0.8% Cu-TiO2 showed the best hydrogen evolution rate of 7245.01 μmol·g−1·h−1, which was 3.57 and 1.34 times of 1.25% MoS2- TiO2 (2726.22 μmol·g−1·h−1) and pristine TiO2 material (2028.46 μmol·g−1·h−1), respectively. These two kinds of composites also had good stability for hydrogen evolution. Combined with the results of photocurrent density and electrochemical impedance spectra, the incorporation of oxygen vacancies and cocatalysts (Cu and MoS2) could not only enhance the light-harvesting of TiO2 but also improve the separation and transfer capabilities of light-induced charge carriers, thus promoting water splitting to hydrogen.

In this work, we investigated the photo-degradation performance of MnO2-SiC fiber-TiO2 (MnO2-SiC-TiO2) ternary nanocomposite according to visible light excitation utilizing methylene blue (MB) and methyl orange (MO) as standard dyes. The photocatalytic physicochemical characteristics of this ternary nanocomposite were described by X-ray diffraction (XRD), scanning electron microscopy (SEM), tunneling electron microscopy (TEM), ultraviolet-visible (UV-vis), diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), photocurrent and cyclic voltammogram (CV) test. Photolysis studies of the synthesized MnO2-SiC-TiO2 composite were conducted using standard dyes of MB and MO under UV light irradiation. The experiments revealed that the MnO2-SiC-TiO2 exhibits the greatest photocatalytic dye degradation performance of around 20 % with MB, and of around 10 % with MO, respectively, within 120 min. Furthermore, MnO2-SiC-TiO2 showed good stability against photocatalytic degradation. The photocatalytic efficiency of the nanocomposite was indicated by the adequate photocatalytic reaction process. These research results show the practical application potential of SiC fibers and the performance of a photocatalyst composite that combines these fibers with metal oxides.

CO2 photocatalytic reduction is a carbon–neutral renewable energy technology. However, this technology is restricted by the low utilization of photocatalytic electrons. Therefore, to improve the separation efficiency of photogenerated carriers and enhance the performance of CO2 photocatalytic reduction. In this paper, g-C3N4/Pd composite with Schottky junction was synthesized by using g-C3N4, a two-dimensional material with unique interfacial effect, as the substrate material in combination with the co-catalyst Pd. The composite of Pd and g-C3N4 was tested to have a strong localized surface plasmon resonance effect (LSPR), which decreased the reaction barriers and improved the electron utilization. The combination of reduced graphene oxide (rGO) created a π–π conjugation effect at the g-C3N4 interface, which shortened the electron migration path and further improved the thermal electron transfer and utilization efficiency. The results show that the g-C3N4/ rGO/Pd (CRP) exhibits the best performance for photocatalytic reduction of CO2, with the yields of 13.57 μmol g− 1 and 2.73 μmol g− 1 for CO and CH4, respectively. Using the in situ infrared test to elucidate the intermediates and the mechanism of g-C3N4/rGO/Pd (CRP) photocatalytic CO2 reduction. This paper provides a new insight into the interface design of photocatalytic materials and the application of co-catalysts.

The untreated effluent dropping into the environment from various textile industries is a major issue. To solve this problem, development of an efficient catalyst for the degradation of macro dye molecules has attracted extensive attention. This work is mainly focused on the synthesis of nickel–manganese sulfide decorated with rGO nanocomposite (Ni–Mn-S/rGO) as an effective visible photocatalyst for degradation of textile toxic macro molecule dye. A simple hydrothermal method was used to synthesize Ni–Mn-S wrapped with rGO. The prepared composites were characterized using various techniques such as X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infra-red spectrometer (FTIR), and ultra violet–visible (UV–Vis) spectroscopy. The photocatalytic performance of nickel sulfide (NiS), manganese sulfide (MnS), nickel–manganese sulfide (Ni–Mn-S), and Ni–Mn-S/rGO nanocomposite was assessed by analyzing the removal of acid yellow (AY) and rose bengal (RB) dyes under natural sun light. Among these, the Ni–Mn-S/rGO nanocomposite showed the high photocatalytic degradation efficiency of AY and RB dyes (20 ppm concentration) with efficiency at 96.1 and 93.2%, respectively, within 150-min natural sunlight irradiation. The stability of photocatalyst was confirmed by cycle test; it showed stable degradation efficiency even after five cycles. This work confirms that it is an efficient approach for the dye degradation of textile dyes using sulfide-based Ni–Mn-S/rGO nanocomposite.

The combination of the two-dimensional (2D) materials g-C3N4 and MXenes in photocatalysis offers several advantages. The g-C3N4 can serve as a visible light-absorbing material, while MXenes can enhance the charge separation and transfer processes leading to improved photocatalytic efficiency. A critical review of 77 already published articles in the field of photocatalytic reactions using g-C3N4 and MXenes, such as hydrogen evolution, the reduction of carbon dioxide, the degradation of organic compounds, the redox reactions of nitrogen, was conducted. For the purpose of greater objectivity, the published results were analysed by non-parametric Mann–Whitney, Kolmogorov–Smirnov, and Mood´s median tests and visualised by box and whisker plots. It was found that MXenes can significantly improve the photocatalytic activity of g-C3N4. Adding other co-catalysts to the MXene/g-C3N4 composites does not bring a significant improvement in the photocatalytic performance. Promising results were obtained especially in the fields of hydrogen evolution and the reduction of carbon dioxide. Since the MXenes are relatively a new class of materials, there is still a big challenge for finding new photocatalytic applications and for the enhancement of existing photocatalytic systems based on g-C3N4, especially in terms of the MXenes and g-C3N4 surface and in the heterojunction engineering.

Fe3O4/g-C3N4/TiO2 catalyst has been fabricated using a simple ultrasonic method with high photocatalytic activity. The morphology, structure and optical properties of Fe3O4/ g-C3N4/TiO2 were systematically investigated by a variety of characterization techniques. The optimum degradation conditions were investigated by degrading tetracycline (TC) under visible light irradiation. The results showed that the degradation efficiency was the highest when the initial TC concentration was 5.0 mg/L, the pH value was 11 and the catalyst dosage was 1.0 g/L. After 100 min of visible light irradiation, the degradation efficiency of TC achieved at 73.61%, which was 1.64 and 1.19 times that of g-C3N4 and Fe3O4/ g-C3N4, respectively. Moreover, Fe3O4/ g-C3N4/TiO2 had good stability and recyclability. The results of capture experiments showed that ‧O2 − and ‧OH were the main active species during the photocatalytic process, and a possible photocatalytic reaction mechanism of Fe3O4/ g-C3N4/TiO2 catalyst was proposed. This study provides a new way to improve the photocatalytic performance of g-C3N4, which has great potential in degrading pollutants such as antibiotics in wastewater.

Pharmaceutical products occurring in freshwater bodies create numerous problems for the water bodies owing to their bio-toxic nature. In order to remove such pharmaceutical pollutants, a novel Er-doped Bi4O5Br2/ g-C3N5 nanocomposite was prepared by one-pot synthesis and applied for the photocatalytic removal process. The Er ions doped on the surface of Bi4O5Br2/ g-C3N5 nanocomposite exhibited 97% degradation of tetracycline in 60 min under visible light irradiation, which is higher than pure g-C3N5 and Bi4O5Br2 photocatalysts. The improved photocatalytic properties are attributed to the outstanding visible light harvesting capacity and quick charge carrier separation efficiency which greatly reduced the recombination rate in the heterojunctions. Based on radical trapping experiments, the •O2 −, h+ and •OH radicals played a prominent role in the photodegradation reactions under visible light. Finally, the ternary Er-doped Bi4O5Br2/ g-C3N5 nanocomposite is effectively recyclable with quite a stable photocatalytic removal rate. This work enables a new perspective on the rational design of rare-earth-based nanocomposites for various pharmaceutical pollutants treatment processes.

Semiconductor-based photocatalytic carbon dioxide ( CO2) reduction is of great scientific importance in the field of alleviating global warming and energy crisis. Surface amine modification and cocatalyst loading on the catalyst surface could improve CO2 adsorption capacity and photogenerated charge separation. Herein, amine-modified brookite–TiO2 ( NH2–B–TiO2) coupled metal species (Cu, Ag, Ni(OH)2) cocatalysts have been successfully synthesized by chemical reduction method. The photocatalytic CO2 reduction results show that the CH4 production rates of NH2– B–TiO2/Cu, NH2– B–TiO2/Ag, and NH2– B–TiO2/Ni(OH)2 are 3.2, 12.5, and 1.7 times that of NH2– B–TiO2 (0.74 μmmol g− 1 h− 1), respectively. Results show the introduction of metal species on the surface of the catalyst enhances the absorption range of sunlight and the photogenerated carrier separation efficiency, resulting in enhancing the performance of photocatalytic CO2 reduction. This work provides a strategy for designing metal species-loaded amine-modified brookite–TiO2 by surface/interface regulation to improve photocatalytic efficiency.

Considering the characteristics of aldehydes among volatile organic compounds, a combined process was established by linking an absorbent and a photocatalytic reactor. Experiments to find the optimal operating conditions of the combined process showed that as the amount of photocatalyst coating increases, the wavelength of the ultraviolet lamp used becomes shorter, the photodegradation rate becomes faster, and the removal efficiency increases. It was also demonstrated that by controlling the relative humidity during the connection process of the combined process, the re-evaporation phenomenon at the front end (absorption area) of the hybrid process can be improved and the removal efficiency at the back end (photocatalytic reaction area) can be significantly enhanced. This confirmed the need for a combined process that complements the advantages and disadvantages of each process.

The emergence of Mo2C- based catalysts in recent years has been favored as promising contender within diverse class MXenes. In terms of rapid development in the photocatalytic application, these intriguing compounds exhibit excellent photocatalytic performance because of their superior optical properties and peculiar structure characteristics. Unfortunately, a systematic review of Mo2C- based catalysts is lacking. In this review, we abstract the implication of structure—property relationship of emerging Mo2C- based MXenes materials and their applications toward the photocatalytic hydrogen evolution reaction (HER). Furthermore, synthetic pathways to prepare high-quality, low cost Mo2C- based MXenes materials and their outcomes for high HER applications are systematically described. Finally, several insights are provided into the prospects and future challenges for the development of highly reactive Mo2C- based MXenes materials, which present large range opportunities in this promising 2D materials for green and clean energy in environmental fields. This review provides a comprehensive scientific guide to the preparation, modification, and photocatalytic HER of MXenes-based materials.

In this study, a bipolar visible light responsive photocatalytic fuel cell (PFC) was constructed by loading a Z-scheme g-C3N4/ carbon black/BiOBr and a Ti3C2/ MoS2 Schottky heterojunction on the carbon brush to prepare the photoanode and photocathode, respectively. It greatly improved the electron transfer and achieved efficient degradation of organic pollutants such as antibiotics and dyes simultaneously in two chambers of the PFC system. The Z-scheme g-C3N4/carbon black/BiOBr formed by adding highly conductive carbon black to g-C3N4/BiOBr not only effectively separates the photogenerated carriers, but also simultaneously retains the high reduction of the conduction band of g-C3N4 and the high oxidation of the valence band of BiOBr, improving the photocatalytic performance. The exceptional performance of Ti3C2/ MoS2 Schottky heterojunction originated from the superior electrical conductivity of Ti3C2 MXene, which facilitated the separation of photogenerated electron–hole pairs. Meanwhile, the synergistic effect of the two photoelectrodes further improved the photocatalytic performance of the PFC system, with degradation rates of 90.9% and 99.9% for 50 mg L− 1 tetracycline hydrochloride (TCH) and 50 mg L− 1 rhodamine-B (RhB), respectively, within 180 min. In addition, it was found that the PFC also exhibited excellent pollutant degradation rates under dark conditions (79.7%, TCH and 97.9%, RhB). This novel pollutant degradation system is expected to provide a new idea for efficient degradation of multiple pollutant simultaneously even in the dark.

Polymeric carbon nitride (p-C3N4) is a promising platform as a metal-free photo-catalyst for various reactions. The p-C3N4 can be produced by thermal poly-condensation of organic precursors. Their morphological and chemical structures depend on reaction conditions during the poly-condensation. In this study, two p-C3N4 materials are produced by heat treatment of urea under different gaseous conditions with air (urea-derived carbon nitride under air, UCN-A) and N2 (UCN-N), respectively. UCN-A and UCN-N samples are mesoporous materials and show excellent photocatalytic activities for degrading rhodamine B, an organic pollutant, under the irradiation of visible light. The UCN-A shows the better photocatalytic activity than UCN-N. Various characterizations reveal that more porous structures and larger surface areas of UCN-A are reasons for the better photocatalytic performance.

The removal of aqueous pollutants, including dye molecules from wastewater remains one of the pressing problems in the world. Because of chemical stability and conjugated structure, dye molecules cannot be easy decomposed by heat with oxidizing reagents such as H2O2 and light. The most common representative of widespread organic pollutant is methylene blue (MB) with molecular formula C16H18ClN3S, which is important colorant and used in various chemical and biological production industries and causes serious environment problems. Porous materials, including MOFs (metal-organic frameworks) have been applied for efficient MB photocatalytic degradation. However, one of the main barriers to using most MOFs to break down aromatic organics is wide band gap energy, which means that the catalyst can exhibit high photocatalytic performance only under UVlight irradiation. Moreover, most MOFs usually show the poor water stability of frameworks, which tend to dissolve in water with total destruction. In this work we report about two new copper based MOFs with high photocatalytic properties for efficient MB degradation from wastewater under UV-light and natural sunlight. Time, required for 100% MB degradation, equals 7 minutes under UV (source 4 W 254 nm VL-4.LC UV-lamp) and 60 minutes under natural sunlight irradiation in the presence of H2O2. Crystal structure information is provided using single crystal X-ray diffraction data. The composition and comparative characteristics of MOFs are given using powder X-ray diffraction, UV–visible diffuse reflectance spectroscopy, UVvisible spectroscopy and Fourier-transform infrared spectroscopy.

The conversion of CO2 into solar fuels by photocatalysis is a promising way to deal with the energy crisis and the greenhouse effect. The introduction of oxygen vacancy into semiconductor has been proved to be an effective strategy for enhancing CO2 photoreduction performance. Herein, TiO2- x nanostructures have been prepared by a simple solvothermal method and engineered by the reaction time. With the prolonging of reaction time, the oxygen vacancy signal gradually increases while the band gap becomes narrow for the as-synthesized TiO2- x nanostructures. The results show that the TiO2- x-6 h, TiO2- x-24 h, and TiO2- x-48 h samples have the main product of CH4 (more) and CO (less) for CO2 photoreduction. Among the three oxygen vacancy photocatalysts, the TiO2- x-24 h sample shows the highest CH4 generation rate of 41.8 μmol g− 1 h− 1. On the basis of photo/electrochemical measurements, the TiO2- x-24 h sample exhibits efficient electron–hole separation and charge transfer capabilities, thus allows much more electrons to participate in the reaction and finally promotes the photocatalytic CO2 reduction reaction. It further confirms that the optimization of oxygen vacancy concentration could facilitate the photoinduced charge separation and accordingly improve photocatalytic CO2 conversion.

Interest in the use of semiconductor-based photocatalyst materials for the degradation of organic pollutants in a liquid phase has grown, due to their excellent performance and response to the light source. Herein, we fabricated a NiO-SiCTiO2 ternary structured photocatalyst which had reduced bandgap energy, with strong activation under UV-light irradiation. The synthesized samples were examined using XRD, SEM, EDX, TEM, DRS, EIS techniques and photocurrent measurement. The results confirmed that the two types of metal oxides were well bonded to the SiC fiber surface. The junction of the new photocatalyst exhibited a large number of photoexcited electrons and holes. The holes tended to oxidize the water and form a hydroxyl radical, which promoted the decomposition of methylene blue. The close contact between the 2D SiC fiber and metal oxide semiconductors expanded the scope of absorption wavelength, and enhanced the usability of the ternary photocatalyst for the degradation of methylene blue. Among three synthesized samples, the NiO-SiC-TiO2 showed the best photocatalytic effect, and was considered to have excellent photoelectron transfer due to the synergy effect between the metal oxide and SiC.