Hydrogen peroxide (H2 O2 ) has received increasing attention because it is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation but also a promising new liquid fuel. The production of H2 O2 by photocatalysis is a sustainable process, since it uses water and oxygen as the source materials and solar light as the energy. Encouraging processes have been developed in the last decade for the photocatalytic production of H2 O2 . In this Review we summarize research progress in the development of processes for the photocatalytic production of H2 O2 . After a brief introduction emphasizing the superiorities of the photocatalytic generation of H2 O2 , the basic principles of establishing an efficient photocatalytic system for generating H2 O2 are discussed, highlighting the advanced photocatalysts used. This Review is concluded by a brief summary and outlook for future advances in this emerging research field.

Production of Hydrogen Peroxide by Photocatalytic Processes

A review of the innovations in metal- and carbon-based catalysts explored for heterogeneous peroxymonosulfate (PMS) activation, with focus on radical vs. non-radical degradation pathways of organic contaminants

Fenton/Fenton-like processes with in-situ production of hydrogen peroxide/hydroxyl radical for degradation of emerging contaminants: Advances and prospects.

Nitrogen-doped carbon materials attract broad interest as catalysts for peroxymonosulfate (PMS) activation toward an efficient, nonradical advanced oxidation process. However, synthesis of N-rich carbocatalysts is challenging because of the thermal instability of desirable nitrogenous species (pyrrolic, pyridinic, and graphitic N). Furthermore, the relative importance of different nitrogenous configurations (and associated activation mechanisms) are unclear. Herein, we report a "coating-pyrolysis" method to synthesize porous 2D N-rich nanocarbon materials (PCN-x) derived from dopamine and g-C3N4 in different weight proportions. PCN-0.5 calcined at 800 °C had the highest surface area (759 m2/g) and unprecedentedly high N content (18.5 at%), and displayed the highest efficiency for 4-chlorophenol (4-CP) degradation via PMS activation. A positive correlation was observed between 4-CP oxidation rates and the total pyridinic and pyrrolic N content. These N dopants serve as Lewis basic sites to facilitate 4-CP adsorption on the PCN surface and subsequent electron-transfer from 4-CP to PMS, mediated by surface-bound complexes (PMS-PCN-0.5). The main degradation products were chlorinated oligomers (mostly dimeric biphenolic compounds), which adsorbed to and deteriorated the carbocatalyst. Overall, this study offers new insights for rational design of nitrogen-enriched carbocatalysts, and advances mechanistic understanding of the critical role of N species during nonradical PMS activation.

2D N-Doped Porous Carbon Derived from Polydopamine-Coated Graphitic Carbon Nitride for Efficient Nonradical Activation of Peroxymonosulfate

Hydrogen peroxide (H2O2) has a wide range of important applications in various fields including chemical industry, environmental remediation, and sustainable energy conversion/storage. Nevertheless, the stark disconnect between today's huge market demand and the historical unsustainability of the currently-used industrial anthraquinone-based production process is promoting extensive research on the development of efficient, energy-saving and sustainable methods for H2O2 production. Among several sustainable strategies, H2O2 production via electrochemical and photochemical routes has shown particular appeal, because only water, O2, and solar energy/electricity are involved during the whole process. In the past few years, considerable efforts have been devoted to the development of advanced electrocatalysts and photocatalysts for efficient and scalable H2O2 production with high efficiency and stability. In this review, we compare and contrast the two distinct yet inherently closely linked catalytic processes, before we detail recent advances in the design, preparation, and applications of different H2O2 catalyst systems from the viewpoint of electrochemical and photochemical approaches. We close with a balanced perspective on remaining future scientific and technical challenges and opportunities.

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A comparative perspective of electrochemical and photochemical approaches for catalytic H2O2 production

Reduced g-C3N4 material was prepared by a thermal treatment of g-C3N4 in presence of NaBH4 under N2 atmosphere. The prepared catalyst material was characterized by using elemental analyzer, FTIR and XPS and the analysis showed that the reduction treatment created nitrogen vacancies followed by a formation of functional group C N owing to a break-up reaction in the pyridine nitride of a s-triazine-C3N4. The findings of UV–vis DRS and DFT calculation revealed that the formed functional group C N results in a narrowed energy band gap owing to positive shift in the conduction band as well as valence band. The downshift observed in the valence band level made the catalyst material with a feature of visible light-driven water oxidation capacity, that was confirmed by the electron and hole sacrifice and OH trapping-EPR techniques. The intermediate energy level within the band gap of g-C3N4 originated from the vacancies caused an extended absorption, especially to the visible region. The analysis of PL emission spectrum confirmed that the reduction treatment could facilitate the spatial separation of photo-excited electron and hole, and enhance the charge transfer as well. RDE studies showed that the selective production of H2O2 by two-electron reduction of O2 was a predominant reaction step using the reduced g-C3N4. The reduced g-C3N4 prepared at 370 °C exhibited an efficient visible light driven catalytic performance on H2O2 production (170 μmol/L h−1) from pure H2O and O2 at ambient atmosphere in the absence of organic electron donors. The solar-to-H2O2 chemical conversion efficiency and apparent quantum yield approached to ∼0.26%, ∼4.3%, respectively. In addition, the experimental results obtained on recycling of the prepared g-C3N4 evidenced the photocatalytic stability of the material.

Visible light-driven photocatalytically active g-C3N4 material for enhanced generation of H2O2

Glucose and melamine derived nitrogen-doped carbonaceous catalyst for nonradical peroxymonosulfate activation

High performance of the A-Mn2O3 nanocatalyst for persulfate activation: Degradation process of organic contaminants via singlet oxygen

Enhanced photocatalytic CO2 reduction with defective TiO2 nanotubes modified by single-atom binary metal components

In the present work, a novel photocatalytic fuel cell (PFC) system involving a dual heterojunction photoelectrodes, viz. polyaniline/TiO2 nanotubes (PANI/TiO2 NTs) photoanode and CuO/Co3O4 nanorods (CuO/Co3O4 NRs) photocathode, has been designed. Compared to TiO2 NTs electrode of PFC, the present heterojunction design not only enhances the visible light absorption but also offers the higher efficiency in degrading Rhodamine B–a model organic pollutant. The study includes an evaluation of the dual performance of the photoelectrodes as well. Under visible-light irradiation of 3 mW cm−2, the cell composed of the photoanode PANI/TiO2 NTs and CuO/Co3O4 NRs photocathode forms an interior bias of +0.24 V within the PFC system. This interior bias facilitated the transfer of electrons from the photoanode to photocathode across the external circuit and combined with the holes generated therein along with a simultaneous power production. In this manner, the separation of electron/hole pair was achieved in the photoelectrodes by releasing the holes and electrons of PANI/TiO2 NTs photoanode and CuO/Co3O4 NRs photocathode, respectively. Using this PFC system, the degradation of Rhodamine B in aqueous media was achieved to an extent of 68.5% within a reaction duration of a four-hour period besides a simultaneous power generation of 85 μA cm−2.

https://www.mdpi.com/2073-4344/8/1/30/pdf

Honghui Pan

Papers

Visible light-driven photocatalytically active g-C3N4 material for enhanced generation of H2O2

Glucose and melamine derived nitrogen-doped carbonaceous catalyst for nonradical peroxymonosulfate activation

High performance of the A-Mn2O3 nanocatalyst for persulfate activation: Degradation process of organic contaminants via singlet oxygen

Enhanced photocatalytic CO2 reduction with defective TiO2 nanotubes modified by single-atom binary metal components

Highly Efficient and Visible Light Responsive Heterojunction Composites as Dual Photoelectrodes for Photocatalytic Fuel Cell