Comparison of different advanced oxidation processes for phenol degradation.

Hydrogen peroxide (H2O2) is of great significance in biological and environmental processes as well as in chemical industry. Even though anthraquinone autoxidation (AO) process has been the major artificial way to produce H2O2, its energy cost and non-green nature have been motivating people to develop more efficient, economic and green technologies as alternatives. Here we demonstrated that photocatalytic H2O2 production at g-C3N4 could be improved by as much as 14 times in the absence of organic scavenger through a carbon vacancy-based strategy. Both the experimental and theoretical calculation results indicated that the creation of carbon vacancies could reduce the symmetry of g-C3N4 and produce the effect of electron delocalization. This will allow g-C3N4 to possess more excitable electrons and a narrower band gap. On the other hand, carbon vacancies provided more sites to adsorb molecular oxygen and thereby help electrons transfer from g-C3N4 to the surface adsorbed O2. More interestingly, the presence of carbon vacancies changed the H2O2 generation pathway from a two-step single-electron indirect reduction to an one-step two-electron direct reduction. This study could not only develop a novel strategy to improve the H2O2 production activity of semiconductors, but also shed light on the deep understanding of the role played by surface defect structure on photocatalytic activity of semiconductor photocatalysts.

/pdf/effective-photocatalytic-h2o2-production-under-visible-light-1cctx1ljj7.pdf

Effective photocatalytic H2O2 production under visible light irradiation at g-C3N4 modulated by carbon vacancies

The application status and potential of three chemical oxidation treatment methods which generate powerful oxidants (hydroxyl radicals): ultraviolet light (UV)/hydrogen peroxide (H2O2) process, Fenton's reagent treatment, and titanium dioxide (TiO2)-assisted photocatalytic degradation, are described and discussed. These oxidation methods are known to effectively degrade and, in several cases, mineralize contaminants ranging from inorganic compounds (such as cyanides) to chlorinated aliphatic compounds and complex aromatic compounds in reaction times on the order of a few minutes to a few hours. Of the three oxidation systems discussed, the technology for the UV/H2O2 process is the most advanced, with numerous successful full-scale treatment units already in existence. Applications of both the Fenton's reagent and TiO2-assisted photodegradation processes are currently being developed, with the concepts proven in numerous laboratory-scale studies for a wide range of contaminants. However, both of t...

Chemical Oxidation Technologies: Ultraviolet Light/Hydrogen Peroxide, Fenton's Reagent, and Titanium Dioxide-Assisted Photocatalysis

As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C3N4; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured from its fascinating physicochemical and photoelectronic structural features. However, certain inherent drawbacks, involving rapid reassembly of photocarriers, low specific surface area and insufficient optical absorption, limit the wide-range applicability of GCN. Generation of 0D point defects mainly by introducing vacancies (C and/or N) into the framework of GCN has spurred extensive consideration owing to their distinctive qualities to manoeuvre substantially, the optical absorption, radiative carrier isolation, and surface photoreactions. The present review endeavours to summarise a comprehensive study on vacancy defect engineered GCN. Starting from the basic introduction of defects and C/N vacancy modulated GCN, numerous advanced strategies for the controlled designing of vacancy rich GCN have been explored and discussed. Afterwards, light was thrown on the various substantial technologies which are useful for characterising and identifying the introduction of defects in GCN. The salient significance of defect engineering in GCN has been reviewed concerning its impact on optical absorption, charge isolation and surface photoreaction ability. Typically, the achievement of defect engineered GCN has been scrutinised toward various applications like photocatalytic water splitting, CO2 conversion, N2 fixation, pollutant degradation, and H2O2 production. Finally, the review ends with conclusions and vouchsafing future challenges and opportunities on the intriguing and emerging area of vacancy defect engineered GCN photocatalysts.

C-, N-Vacancy defect engineered polymeric carbon nitride towards photocatalysis: viewpoints and challenges

The use of ozonation to degrade organic contaminants in wastewaters

Treatment of bleaching waters in the paper industry by hydrogen peroxide and ultraviolet radiation

Ozonization of bleaching waters of the paper industry

This study examines the use of ozone and ozone/ultraviolet radiation treatments of a kraft bleach plant effluent proceeding from the bleaching stages for kraft pulp decolorization. An outline for the reaction is proposed in which the oxidizable compounds of the effluent are grouped into three classes: easily degradable colored compounds, colored compounds of difficult degradation, and uncolored compounds

Claustre Prat

Papers

Treatment of bleaching waters in the paper industry by hydrogen peroxide and ultraviolet radiation

Ozonization of bleaching waters of the paper industry

Ozone and ozone/uv decolorization of bleaching waters of the paper industry

Influence of lamp position on available radiation flux in an annular photoreactor