Mass Production and High Photocatalytic Activity of ZnS Nanoporous Nanoparticles

TLDR: Recent studies have revealed that ZnS nanocrystals (NCs) are good photocatalysts as a result of the rapid generation of electron– hole pairs by photoexcitation and the highly negative reduction potentials of excited electrons, and an irreversible two-electron-transfer photoreduction of organic substrates.

Abstract: Environmental problems associated with organic pollutants and toxic water pollutants provide the impetus for sustained fundamental and applied research in the area of environmental remediation. Semiconductor photocatalysis offers the potential for complete elimination of toxic chemicals through its efficiency and potentially broad applicability. [1] Various new compounds and materials for photocatalysis have been synthesized in the past few decades. A successful example is TiO2, a metal oxide often used as a catalyst in photochemistry, electrochemistry, environmental protection, and in the battery industry. [2] Recently, transition-metal sulfides, in particular ZnS and CdS, have been intensively studied because of their unique catalytic functions compared to those of TiO2. [2, 3] These studies have revealed that ZnS nanocrystals (NCs) are good photocatalysts as a result of the rapid generation of electron– hole pairs by photoexcitation and the highly negative reduction potentials of excited electrons. The photocatalytic properties occur not only in the photoreductive production of H2 from water and the photoreduction of CO2, [4] but also in the phototransformation of various organic substrates such as the oxidative formation of carbon–carbon bonds from organic electron donors, cis–trans photoisomerization of alkenes, and the photoreduction of aldehydes and their derivatives. [5] The notable finding in nonmetalized ZnS photocatalysis is an irreversible two-electron-transfer photoreduction of organic substrates. [6] A favorable shift of the optical response into the visible region occurs subsequent to the doping of transition metal or rare-earth metal ions, such as Ni 2+ and Cu 2+ ; therefore, ZnS NCs can also be used as effective catalysts for photocatalytic evolution of H2 and photoreduction of toxic ions under visible-light irradiation. [7] An important application of ZnS is as a photocatalyst in environmental protection through the removal of organic