Search

Pollution and the rising energy demand are two major society issues, requiring urgent solutions. Here, we review the simultaneous production of hydrogen and removal of pollutants, with a focus on mechanisms, synthesis of photocatalysts, and applications. Remarkably, this method utilizes organic pollutants as sacrificial agents for photocatalytic hydrogen production, thus both reducing pollution and producing energy. Metal-doped, cocatalyst-loaded, organic and inorganic composite, heterostructure and heterojunction photocatalysts are described. We present applications to the removal of antibiotics and organic dyes. Pollutant degradation rates range from 5.3 to 100%, with hydrogen evolution of 13.7–2724.89 μmol·g–1h–1. [ABSTRACT FROM AUTHOR]

Dihydrogen (H2), commonly named "hydrogen", is attracting research interest due to potential applications in fuel cells, vehicles, pharmaceuticals and gas processing. As a consequence, the recent discoveries of natural gas reservoirs have prompted the development of technologies for methane conversion to hydrogen. In particular, the catalytic decomposition of methane is a promising technology to generate COx-free hydrogen and multi-wall carbon materials. Carbon nanomaterial byproducts can be used in electronics, fuel cells, clothes, and for biological and environmental treatments. Recent research has investigated the performance of hydrogen production and the characteristic of carbon nanomaterials. Here, we review the decomposition of methane on Ni-based catalysts, with focus on the influence of reaction temperature, gas hourly space velocity, support, and promoter. Ni-based catalysts allow CH4 conversion higher than 70% with H2 yield of about 45% at more than 700 °C. We present catalyst regeneration by various techniques such as combustion. Reactors used for catalytic decomposition of methane include fluidized bed, fixed-bed and plasma reactors. [ABSTRACT FROM AUTHOR]

Energy shortage and escalating pollution are major challenges globally. Heterogeneous photocatalysis is one of the most cost-effective methods for producing renewable energy and removing pollutants. In particular, ZnO nanostructures are promising photocatalysts that are economic, stable, and biologically safe. ZnO-based nanoheterostructures have been used for heavy metal reduction, organic pollutants degradation, photocatalytic hydrogen production, and drug mineralization. Here, we review ZnO-based nanoheterojunctions as photocatalysts for hydrogen production and pollutant degradation. Hydrogen production has reached 1200 mol g−1 h−1 using Ce-doped ZnO/ZnS heterojunction, with a 8.5-fold higher efficiency than bare ZnO. Nearly complete removal of a dye pollutant was achieved in 15 min using hybrid ethyl cellulose-modified g-C3N4/ZnO. Moreover, ZnO/Ag2WO4/Fe3O4 showed a 152% and 143% higher antibiotic degradation rate than bare Ag2WO4 and ZnO, respectively. We present methods to modify ZnO, including coupling with other semiconductors, metal/non-metal doping, and carbon-based materials coupling; and methods for charge divergence in binary and ternary ZnO-based nanocomposites. [ABSTRACT FROM AUTHOR]

Providing sustainable energy and cleaning water pollution are actually major societal issues requiring new catalysts. In particular, transition metal phosphides are emerging as effective photocatalytic materials. Here we review synthetic strategies for metal phosphides by various methods. We discuss passivation strategies for engineering electronic and structural properties of metal phosphide nanocomposites. Electronic properties, stability and activity depend upon the type of metal phosphides, either phosphorus-rich or metal-rich. Typically, a high content of phosphorous in metal phosphides improves the catalysis. The crystalline structure of metal phosphides also varies and depends upon their chemical composition. We present the latest developments in H2 production and photodegradation of aqueous pollutants using metal phosphide-based heterojunctions, with focus on type-II-, Z-scheme- and S-scheme-based heterojunctions. [ABSTRACT FROM AUTHOR]

Effective technologies and materials are needed for environmental detoxification and clean energy production. The actual photocatalytic technology is largely dependent on metal oxide-based semiconductors, which have issues such as cost, limited spectral response and recombination problems. Alternatively, non-metal photocatalysts have recently emerged. This article reviews non-metal oxide photocatalytic materials such as carbon nitride, metal nitrides, phosphides, chalcogenides, perovskites and carbides for environmental clean-up and energy production. [ABSTRACT FROM AUTHOR]

Environmental pollution and climate change are requiring new methods to clean pollutants and produce sustainable energy. Aerogels and metal organic frameworks are emerging as advanced porous materials with higher functionality, high surface area, high porosity and flexible chemistry. Aerogels are dried gels prepared using the sol-gel procedure, whereas metal organic frameworks are networks of organic ligands and metal ions connected by coordination bonds. Applications of aerogels include the removal of heavy metals, CO2 capture and reduction, photodegradation of pollutants, air cleanup and water splitting. This article reviews the synthesis and types of aerogels and metal organic frameworks, and the application to pollutant removal, energy production including hydrogen, methane reforming, CO2 conversion and NOx removal. [ABSTRACT FROM AUTHOR]

Human activities such as industrialisation, urbanisation and agriculture have adversely impacted terrestrial and aquatic ecosystems. Water pollutants such as heavy metals and nanoparticles can undergo bioaccumulation and bioaugmentation. Heavy metals cannot be degraded and are hence added permanently. Nanoparticles are a potential threat because of their small size and unique properties. This article reviews the impact of various pollutants on aquatic biota and presents remediation methods. Benthic macroinvertebrates can be used as bioindicators to study the impact of pollutants on aquatic ecosystems. Fishes occupy the highest trophic level in the aquatic food chain and can therefore accumulate large amounts of metal from water, ultimately leading to biomagnification. Some organic compounds such as pesticides and fungicides are carcinogenic and sometimes resistant to degradation. [ABSTRACT FROM AUTHOR]

Nanocomposite hydrogels are polymeric networks that possess a unique property of hydration. The presence of alcohols, carboxylic acids and amides as hydrophilic moieties in structure of nanocomposite hydrogels enhances their stiffness and water-absorbing capacity. Addition of cross-linker in the synthesis of hydrogels increases their stability under extreme conditions of temperature, pH and pressure. Natural polymer-based nanocomposite hydrogels are biodegradable, highly hydrophilic and possess good mechanical strength. Gelatin, chitin, cellulose, pectin, carrageenan, starch and alginate are natural polymers commonly used to fabricate nanocomposite hydrogels. Nanocomposite hydrogels have special characteristics such as high swelling rate, selectivity and stimuli-sensitive nature. Here we review nanocomposite hydrogels for environmental protection and biomedical engineering. Applications in biomedical engineering include drug delivery agents, wound dressing, tissue engineering and antibacterials. Applications in environmental protection include ion exchangers, adsorption, photocatalysis and soil conditioning. Many nanocomposite hydrogels show excellent adsorption selectivity for heavy metal ions: Cu2+ up to 30.35 mg/g, Pb2+ up to 35.94 mg/g, and Zn2+ and Fe3+ up to 94.34 mg/g. Xanthan gum-based nanocomposite hydrogel has removed 96% dye from industrial effluent as reported. In addition, most of the nanocomposite hydrogels showed better adsorption capacity for pollutants in the pH range from 5 to 7. The nanocomposite hydrogels could also be regenerated and successfully utilized for several times. Nanocomposite hydrogels are therefore good bio-absorbent materials for environmental detoxification. [ABSTRACT FROM AUTHOR]