Removal of Chromium Species by Adsorption: Fundamental Principles, Newly Developed Adsorbents and Future Perspectives.

Emerging chromium (Cr) species have attracted increasing concern. A majority of Cr species, especially hexavalent chromium (Cr(VI)), could lead to lethal effects on human beings, animals, and aquatic lives even at low concentrations. One of the conventional water-treatment methodologies, adsorption, could remove these toxic Cr species efficiently. Additionally, adsorption possesses many advantages, such as being cost-saving, easy to implement, highly efficient and facile to design. Previous research has shown that the application of different adsorbents, such as carbon nanotubes (carbon nanotubes (CNTs) and graphene oxide (GO) and its derivatives), activated carbons (ACs), biochars (BCs), metal-based composites, polymers and others, is being used for Cr species removal from contaminated water and wastewater. The research progress and application of adsorption for Cr removal in recent years are reviewed, the mechanisms of adsorption are also discussed and the development trend of Cr treatment by adsorption is proposed.

Theoretical Investigation of the Reaction of Imidogen with Fulminic Acid.

The mechanism of the reaction of imidogen (NH) with fulminic acid (HCNO) has been investigated theoretically using the multiconfigurational self-consistent-field theory (MCSCF), multireference Rayleigh-Schrodinger perturbation theory (RSPT2), and coupled cluster theory (CC) along with the complete basis set extrapolations (CBS). The calculations show that the NH + HCNO reaction takes place via an N → C addition mechanism predominantly by surmounting a small barrier (ca. ∼3 kcal/mol). The adduct is HC(NH)NO in the triplet state with an exothermicity of more than 60 kcal/mol. The subsequent C-N cleavage, which is nearly barrierless, leads to HCNH and NO as the final products. This represents the most energetically favorable product channel of the title reaction. The channels leading to HCN, HNC, HNO, or HON via O- or H-migration mechanisms involve higher barriers and thus are negligible. The singlet-triplet crossing has been investigated as well for the HCNH + NO product channel by locating the conical interactions. Using transition state theory, the rate constants were predicted as a function of temperatures. It is suggested that the NH + HCNO reaction might be an alternative source for the NO regeneration under the combustion conditions. This calculation is useful to simulate experimental investigations of the NH + HCNO reaction.