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Hydrogen peroxide (H2O2) is a mild, environmentally friendly, and versatile oxidizer. The current main production process, the anthraquinone method, has high energy consumption and pollution. However, the photocatalytic production of H2O2 is considered to be a green and sustainable process. In this paper, the research progress of photocatalytic production of H2O2 was reviewed. Firstly, the basic principle of photocatalytic production of H2O2 and the three production pathways, namely, oxygen reduction, water oxidation, and dual-channel were introduced. Then, advanced photocatalysts for H2O2 production were introduced with emphasis. From the reactants and products, several new reaction systems and improvement strategies were introduced, including the construction of a spontaneous system without a sacrifice agent, a gas–liquid–solid three-phase system, and inhibition of H2O2 decomposition. The in-situ applications of photocatalytic H2O2 production in the environmental field, including in-situ disinfection and in-situ degradation of pollutants are discussed. Finally, the research progress and future research directions in this field are summarized and prospected. [ABSTRACT FROM AUTHOR]

Single-site heterogeneous catalysts constructed with highly dispersed, spatially well-separated isolated species have attracted much attention due to their outstanding specific activity and selectivity attributable to the unsaturated surface coordination sites and unique local electronic structures. Furthermore, such single-site heterogeneous catalysts are considered to be attractive as models for the top surface of inorganic semiconducting materials. As catalysts and photocatalysts, they provide suitable reaction fields to investigate the relationship between the activity and local structure of the active sites. To obtain detailed information on the reaction mechanism at the molecular level, advanced characterization techniques such as X-ray absorption fine-structure spectroscopy (XAFS), FT-IR, UV–VIS, EPR, and photoluminescence spectroscopy were applied. Moreover, various solid materials such as silica, mesoporous materials including zeolites, and semiconducting materials offer applicable strategies to design unique single-site heterogeneous photocatalysts. In the present review, photocatalytic reactions on single-site heterogeneous catalysts constructed on semiconducting materials have been summarized. Special attention has been focused on photocatalytic reactions for clean energy such as the splitting of water, reduction of carbon dioxide with H2O, conversion of CH4, and fixation of nitrogen. Furthermore, the preparation of single-site heterogeneous catalysts, their characterizations, and the relationship between their local structures and photocatalytic activities are also discussed. The present review not only provides a systematic understanding of single-site heterogeneous photocatalysts but also an understanding of the reaction mechanisms of semiconducting photocatalysis at the atomic level as well as the design of high-performance catalytic and photocatalytic reaction systems. [ABSTRACT FROM AUTHOR]

Photocatalytic treatment of water pollutants has attracted extensive attention due to its low energy consumption, low cost and the avoidance of secondary environmental pollution. However, most photocatalysts are in powder form, which makes it difficult to separate from the water system after the reaction. Especially in practical applications, the recycling of the catalyst is an important part. Based on the characteristics that sodium alginate (SA) is easy to form gels under mild conditions, GO-P25@SA gel beads were prepared. The catalyst can be separated from the water system by simple filtration, which greatly saves the recycle cost. Besides, the light response of TiO2 (P25) and excellent conductivity of graphene oxide (GO) make GO-P25@SA have excellent photocatalytic degradation and cyclic stability for rhodamine B (RhB). In this work, the unique merits of GO and sodium alginate (SA) in developing functionalized photocatalyst were demonstrated, providing a low-cost and easy recycle treatment strategy for rhodamine B degradation. [ABSTRACT FROM AUTHOR]

Amorphous MoO3−x nanosheets were fabricated by the room‐temperature oxidation of molybdenum powder with H2O2, followed by light‐irradiation reduction in methanol. When applied as a substrate for surface‐enhanced Raman spectroscopy (SERS), these nanosheets exhibit higher sensitivity than the crystalline counterpart for a wide range of analytes. Moreover, the SERS activity remains stable on repeated oxygen insertion/extraction. In contrast, the performance of crystalline MoO3−x continuously deteriorates on successive redox treatments. This unique SERS activity allows the recycling of the substrate through an H2O2‐based Fenton‐like reaction. More importantly, the non‐invasive SERS was unprecedentedly used for the self‐diagnosis of amorphous MoO3−x as a more selective photocatalyst than its crystalline counterpart. [ABSTRACT FROM AUTHOR]

The development of high-efficiency economic photocatalyst for H2O2 production is of great significance for renewable energy technologies. Here, we use a successive in situ growth and phosphating method successfully prepared NiCoP/g-C3N4 composite photocatalyst. NiCoP was uniformly dispersed in the form of nanoparticles on the surface of g-C3N4 nanosheet as a cocatalyst. The obtained NiCoP/g-C3N4 composite showed excellent performance in photocatalytic production of H2O2, which was due to NiCoP, has a better electronic conductivity to efficiently transfer charge, improves charge separation efficiency and enhances visible light absorption. This study can provide an effective theoretical basis for the design of bimetallic phosphide modified photocatalysts for photocatalytic production of H2O2. [ABSTRACT FROM AUTHOR]

The utilization of TiO2-based photocatalysts for an efficient removal of dye pollutants is limited due to their low surface area, high recombination rate of the photo-generated electrons and holes and an insufficient absorption of sunlight with only 3–4% use of solar energy. Based on this background, we have successfully fabricated a carbon nitride quantum dots (CNQDs)-modified mesoporous TiO2–SiO2 (Me-TSCN) via a simple calcination method since the mesoporous structure is expected to induce a great increase in the specific surface area by carbon nitride quantum dots, being favorable for the adsorption of the reactant molecules and the mass transfer of the reaction products. Furthermore, such CNQD modification facilitates the separation of photo-generated electrons and holes. As a result, the composite's modification with structural design could significantly improve the photocatalytic activity of TiO2-based catalysts, achieving outstanding photocatalytic activity in the degradation of dye pollutants such as rhodamine B. [ABSTRACT FROM AUTHOR]

A composite catalyst combining CoP with g-C3N4 was explored for the photocatalytic production of H2O2 under visible-light irradiation. The composite catalyst was fabricated by growth of CoP nanoparticles on the surface of g-C3N4. The CoP nanoparticles were well dispersed on the surface of g-C3N4 and could interact with g-C3N4 to improve charge separation and electron transfer. The composite catalyst showed superior catalytic activity compared with pure CoP or g-C3N4 under visible-light irradiation. The optimal catalyst with 1.76 wt.-% CoP loading exhibited the best photocatalytic efficiency with an H2O2 production of 140 µm in 2 h, which is about 4.6 and 23.3 times those of pure g-C3N4 and pure CoP, respectively. A possible mechanism for the visible-light-driven photocatalytic production of H2O2 is proposed. The composite catalyst exhibited stable performance without obvious loss of catalytic activity after seven successive runs, and thus has good application prospects in sustainable H2O2 production. [ABSTRACT FROM AUTHOR]

The development of highly active, cost-effective, environmentally friendly and stable g-C3N4 based photocatalysts for H2 evolution is one of the most anticipated potential pathways for future hydrogen utilization. Herein, a facile gaseous bubble template approach was designed to prepare large-scale thin g-C3N4 nanosheets (g-C3N4 NSs) using melamine and ammonium sulphate as the bubble template. Through distinctive structural improvements for a large bandgap, excellent electron mobility, prolonged lifetime of the photogenerated charge carriers and a high specific surface area with highly accessible potential reaction sites, the as-synthesized g-C3N4 NSs demonstrated a high photocatalytic hydrogen evolution rate of 9871 μmol h−1 g−1 and efficient photocatalytic degradation of Rhodamine B (RhB) and phenol under simulated solar light irradiation. [ABSTRACT FROM AUTHOR]

A novel heterojunction photocatalyst with well-dispersed TiO 2 nanoparticles on Co-Doped g-C 3 N 4 has been successfully fabricated by an in situ generation solvothermal method. The photocatalytic performance of the as-prepared TiO 2 /Co-g-C 3 N 4 catalyst was evaluated by the degradation of phenol in the presence of Cr 6 + under simulated sunlight irradiation. The catalyst exhibited markedly enhanced photocatalytic activity for degradation of phenol but obviously decreased photocatalytic activity for reduction of Cr 6 + compared with common TiO 2 /g-C 3 N 4 catalyst. The mechanism for this photocatalytic performance was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • An up-to-date review deciphering the photocatalytic non-oxidative coupling of methane. • Related photocatalysts into four categories were classified. • Noble metal-based photocatalysts show better performance and become a research hotspot. • Considerable guidance for the design of efficient photocatalysts is provided. The importance of effectively converting methane to hydrogen and high value-added hydrocarbons chemicals is becoming more significant due to the huge resources of methane and increasing demands for chemicals. However, it is hard to convert methane into more useful hydrocarbons and hydrogen due to the enormous thermodynamic barrier, which often needs high energy and often results in catalyst deactivation and unsatisfactory product selectivity. Recently, a growing number of researches focusing on photocatalytic methane conversion under mild conditions have attracted much attention, demonstrating that photocatalytic non-oxidative coupling of methane (PNOCM) is a prospective and green method for methane conversion under mild conditions. Herein, we provide a review of the recent advance, remaining challenges, and prospects in PNOCM. Moreover, this review provides considerable guidance for rational design of efficient and stable photocatalysts towards PNOCM by theory predictions and experiment results. We hope this review can attract more attention to the important research field of energy conversion. [ABSTRACT FROM AUTHOR]

A photodeposition method was employed to distribute NiS nanoparticles evenly on the surface of tubular graphitic carbon nitride (TCN). The Schottky junction which was formed spontaneous between NiS and TCN help accumulate electrons on NiS. This effectively weakens the S H bonds and facilitates the desportion of intermediate hydrogen species during hydrogen evolution reaction, leading to superior hydrogen evolution activity. [Display omitted] As one of the most promising photocatalysts for H 2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H 2 evolution rate of 752.9 μmol g−1 h−1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the S H bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H 2 evolution activity. [ABSTRACT FROM AUTHOR]

Bi2WO6 was modified with MnO x via a photodeposition method. Multiple techniques including XRD, SEM, TEM, UV-vis and XPS were applied to investigate the structures, morphologies and optical characteristics of the as-prepared sample. The nanostructured composites were formed with MnO x loaded on the surface of flower-like Bi2WO6, where MnO x exists as a mixed-valence manganese of Mn3+ and Mn4+ as verified by XPS. The photocatalytic activity of the MnO x/ Bi2WO6 composites was evaluated by using rhodamine B ( RhB) as a target organic pollutant under visible light irradiation. The as-prepared MnO x/ Bi2WO6 composites exhibited much higher photocatalytic activities than pure Bi2WO6. The enhanced activities were attributed to the interfacial transfer of photogenerated holes from Bi2WO6 to MnO x, leading to effective way to improve photocatalytic efficiency, which may be extended to a strategy for other semiconductor. Based on the experimental results, a possible mechanism of MnO x for the enhancement of visible light performance was proposed. [ABSTRACT FROM AUTHOR]

Bi2WO6 was modified with MnO x via a photodeposition method. Multiple techniques including XRD, SEM, TEM, UV-vis and XPS were applied to investigate the structures, morphologies and optical characteristics of the as-prepared sample. The nanostructured composites were formed with MnO x loaded on the surface of flower-like Bi2WO6, where MnO x exists as a mixed-valence manganese of Mn3+ and Mn4+ as verified by XPS. The photocatalytic activity of the MnO x/ Bi2WO6 composites was evaluated by using rhodamine B ( RhB) as a target organic pollutant under visible light irradiation. The as-prepared MnO x/ Bi2WO6 composites exhibited much higher photocatalytic activities than pure Bi2WO6. The enhanced activities were attributed to the interfacial transfer of photogenerated holes from Bi2WO6 to MnO x, leading to effective way to improve photocatalytic efficiency, which may be extended to a strategy for other semiconductor. Based on the experimental results, a possible mechanism of MnO x for the enhancement of visible light performance was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ru x P/PCN photocatalyst which completely phosphatized ultrafine ruthenium coupled with g-C 3 N 4 nanosheets were prepared. • P+ centers were formed with the excessive doping P elements to accumulate photo-generated carriers. • Photo-generated charge carriers were separated and transferred through the chemical bridge between PCN and Ru x P NPs. • The prepared sample showed a high photocatalytic activity for photocatalytic hydrogen evolution. Many researches have shown that phosphorus doping can affect the photocatalytic activity, mainly because the incorporation of P atoms significantly alters the electronic, surface chemical, and properties of different semiconductors. However, excessive phosphorous doping will form the accumulation and recombination center of photo-generated charge carrier, thereby limiting the activity of photocatalytic reactions. In this work, we successfully prepared excessive P-doping g-C 3 N 4 with ruthenium phosphide nanoparticles (Ru x P/PCN), which had excellent performance of hydrogen evolution (1.94 mmol g−1 h−1). Specifically, C was replaced by P in the melon units of PCN and positive charge center (P+) was introduced, reinforcing the chemical connection between PCN and Ru x P. In fact, excessive P+ centers became the traps and stacking centers of photo-generated carriers. However, due to the introduction of Ru x P NPs, the accumulated charges in the P+ centers through the chemical bridges between PCN and Ru x P NPs migrated to surface and then separated on Ru x P NPs. Our research illustrates the mechanism of the accumulated charges caused by excessive phosphorus doping migrate to the surface and separate on phosphides, which can prolong the lifetime of photo-generated carriers. This result promoted the significant increase of photocatalytic hydrogen production activity. Our research clarifies the mechanism of excessive phosphorus doping and phosphides act on this photocatalytic system, which will provide a new way to design a photocatalytic system with higher HER performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co 3 O 4 /PDA was designed for PMS activation under NIR light for the first time. • Co 3 O 4 could activate PMS and PDA could accelerate Co2+/Co3+ redox cycle. • Both Co 3 O 4 and PDA could convert NIR light into heat to boost the PMS activation. • A higher LEV degradation rate was achieved in Co 3 O 4 /PDA + PMS + NIR system. The utilization of near-infrared (NIR) light with strong photothermal effect in photo-Fenton or Fenton-like systems for the degradation of organic pollutants is always ignored. In this study, we have synthesized a novel photothermal Fenton-like catalyst (Co 3 O 4 /PDA) to activate peroxymonosulfate (PMS) for the degradation of antibiotics. The Co 3 O 4 in the nanocomposite acts as a PMS activator, while unexpectedly, PDA was found to accelerate the redox cycle of Co2+/Co3+. Both Co 3 O 4 and PDA are black-colored photothermal materials with excellent NIR absorption properties. During the degradation process, the light-to-heat conversion ability of Co 3 O 4 and PDA enables a higher temperature, which innovatively boosts the rate of PMS catalytic activation. Mechanistic studies revealed that the increased temperature effectively promotes the heterogeneous catalytic PMS activation by Co 3 O 4 /PDA. As a result, the Co 3 O 4 /PDA + PMS + NIR system exhibits greatly enhanced degradation performance. Furthermore, this degradation system demonstrates strong tolerance to different operation conditions, and the catalyst exhibits good stability in cycling tests. These results demonstrate the favorable application prospects of this photothermal Fenton-like system in environmental water remediation. The findings also contribute valuable insights towards the development of efficient strategies for the photothermal activation of PMS. [ABSTRACT FROM AUTHOR]

Titanate nanowire has been explored as a precursor for the preparation of TiO 2 catalysts with controllable morphologies by a facile hydrothermal method with HF and urea as assistants. During the hydrothermal process, HF erodes the titanate nanowires to form TiF 6 2− ions, and urea generates OH − in situ to initiate the hydrolysis of TiF 6 2− . The morphology of TiO 2 products can be tuned by simply adjusting the experimental parameters, such as the amounts of HF and urea, reaction time, reaction temperature and the concentration of titanate precursor. The photocatalytic activity of TiO 2 catalysts with different morphologies were evaluated by the photocatalytic degradation of Rhodamine B (RhB) and methyl orange (MO). The experimental results have demonstrated that catalysts with different morphologies have different photocatalytic activities. Along with many advantages of the synthesis process, such as being surfactant-free and easy to operate, the synthesis method developed in this study provides a new inspiration for further investigation into the preparation of TiO 2 catalysts with advanced structures and high photocatalytic activity. [ABSTRACT FROM AUTHOR]

Carbon dots (CD) and Ti species were assembled in the mesoporous silica matrix by a one-pot co-condensation strategy. The CD and Ti in the silica matrix were demonstrated to interact in two ways: on the one hand, part of the carbon in CD was doped into the Ti species; on the other hand, CD worked as photosensitizers for Ti species. The synergy effect between CD and Ti in the silica matrix along with the unique physical properties of the composite including ordered pore channels, large surface area and wide-range light absorption from UV to near IR made this composite be an excellent photocatalyst, as demonstrated by the photocatalytic degradation of azo dye acid orange 7. In addition to the degradation of organic pollutant, this newly developed mesoporous composite is expected to have promising applications in various areas related to environment and energy such as photoreduction of CO 2 and photocatalytic H 2 production. [ABSTRACT FROM AUTHOR]

Mixed-phase TiO 2 photocatalysts with different proportions of anatase and rutile have been successfully synthesized in an acidic hydrothermal system, using tartaric acid (C 4 H 6 O 6 ) as a phase content regulator and titanium trichloride (TiCl 3 ) as the titanium source. The obtained samples were characterized by X-ray diffraction spectroscopy (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and so on. The phase contents of anatase and rutile in the TiO 2 particles were successfully controlled by simply adjusting the molar ratio of C 4 H 6 O 6 to TiCl 3 . And the regulation degree could be further controlled by the concentration of sodium chloride (NaCl) in the reaction system. In addition, the effect of the reaction time, hydrothermal temperature and acidity on the phase structure of as-prepared products have also been investigated. A mechanism was proposed to interpret the evolution of the phases based on the experimental results. Finally, the photocatalytic activity of the prepared TiO 2 were evaluated by the degradation of Rhodamine B (RhB) and methyl orange (MO) in aqueous solutions. The mixed-phase TiO 2 exhibited higher activity than pure phase TiO 2 , and the catalyst containing 77% anatase and 23% rutile had the highest photocatalytic activity. The enhanced photocatalytic activity could be explained by the mixed-phase effect between anatase and rutile. [ABSTRACT FROM AUTHOR]

g-C 3 N 4 modified TiO 2 composites were prepared through a simple calcination process of anatase and cyanamide. The as-prepared samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectrophotometry (DRS), fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermogravimetry differential thermal analysis (TG–DTA) and X-ray photoelectron spectroscopy (XPS), proving a successful modification of TiO 2 with g-C 3 N 4 . Photodegradation of acid orange 7 (AO7) was used to evaluate the photocatalytic activities of the composites, showing excellent activity of them under both visible and UV light. In addition, base treatment was then introduced to investigate the interaction between g-C 3 N 4 and TiO 2 . After removing the g-C 3 N 4 modified on TiO 2 by base, no nitrogen doping is found in TiO 2 lattice, demonstrating the g-C 3 N 4 was surface attached on TiO 2 and attributing all improvement of photocatalytic activity of g-C 3 N 4 /TiO 2 composite to the synergy between the two semiconductors. [ABSTRACT FROM AUTHOR]

Hierarchical macro–mesoporous silica materials co-incorporated with Cr and Ti were directly synthesized by adopting close-packed array of polystyrene microsphere as hard template for macropore through a simple soaking-calcination way, where Si/Ti ratio was fixed at 200 and Si/Cr ratio was set between 200 and 10. Ti specie is highly dispersed in porous matrix and Cr specie mainly exists as tetra-coordinated CrO 3 at higher Si/Cr ratio (Si/Cr ≥ 50), which transforms to a mixture of CrO 3 and crystallized hexa-coordinated Cr 2 O 3 when Si/Cr ratio is below 50. This highly interconnected porous material co-incorporated with Cr and Ti presents highest visible-light driven photocatalytic activity at Si/Cr = 20 toward degradation of AO7. Moreover, macro–mesoporous photocatalyst presents higher activity than those of macroporous and mesoporous ones at the same Si/Cr ratio. The improved visible light driven catalytic activity is mainly attributed to effective metal to metal charge transfer from Cr(VI) to Ti(IV) benefitted from the uniform dispersion of these two species in hierarchical porous silica matrix. [ABSTRACT FROM AUTHOR]

A strategy combining generation promotion and self-decomposition suppression for H 2 O 2 production is developed by utilizing hydroxyls-grafted g-C 3 N 4 nanotube. • g-C 3 N 4 nanotube with in situ Grafted OH was prepared by rational experimental method. • The metal-free ACNT catalyst shows ultra high H 2 O 2 production in spontaneous system. • The nanotube structure and surface OH synergistic promote the H 2 O 2 production. • Multipe mechanisms of action for surface OH are studied and proposed. An active and inexpensive photocatalyst for H 2 O 2 production is desirable for industrial applications. However, obtaining high photocatalytic activity from metal-free catalysts without the use of sacrificial electron donors is difficult. Herein, g-C 3 N 4 (CN) nanotubes functionalized with surface > OH groups that are grafted in situ were successfully synthesized via a novel alkalinization process. The nanotube structures provide a large surface area and improved mass transfer properties. In situ grafted > OH groups can capture photogenerated holes to promote separation of photogenerated charge, enabling the ready availability of electrons and hydrogen ions for H 2 O 2 production. Further, the surface > OH groups help to suppress H 2 O 2 self-decomposition. Consequently, a high rate of 240.36 μmol h−1 g−1 of H 2 O 2 production can be achieved without sacrificial agents, which is the highest H 2 O 2 production in a spontaneous system for metal-free photocatalysts. This work provides a new strategy for an efficient and spontaneous H 2 O 2 production method using a metal-free CN photocatalyst. [ABSTRACT FROM AUTHOR]

• Ultrathin g-C 3 N 4 nanosheets with hierarchical pores and desirable energy band for H 2 O 2 production has been prepared. • A high H 2 O 2 production rate of 1083 μmol g−1 h−1 has been achieved. • The optimization of energy band via P doping changed the reaction route for H 2 O 2 production. • Unique morphology acts in synergy with suitable energy band to enhance the H 2 O 2 production. H 2 O 2 production through photocatalysis has been considered as a sustainable technique. Here, we report ultrathin g-C 3 N 4 nanosheets with hierarchical pores and desirable energy band for high-efficiency photocatalytic H 2 O 2 production. The resultant catalyst showing an ultra-high H 2 O 2 production rate of 1083 μmol g−1 h−1, which is about seven times higher than that of bulk g-C 3 N 4 and represents one of the most active photocatalysts for H 2 O 2 production. DFT calculation and experimental studies revealed that the suitable energy band structure achieved by a phosphorus doping in g-C 3 N 4 leading to the efficient yielding two-electron reduction of O 2 to form H 2 O 2. Meanwhile, the particular morphology provided a large accessible surface area, multi-mass transport channels and short charge transfer distance. The synergy effect of desirable energy band and hierarchical porous nanosheets bring the excellent photocatalytic activity. In addition, the simple preparation procedure and the non-metal properties make it have great potential for the practical application. [ABSTRACT FROM AUTHOR]