A representative polyoxometalate, alpha-12-tungstophosphatic acid (PW12(3-), POM), is loaded on the surface of TiO2 particles used as a cocatalyst to gain further insights into the underlying reaction mechanism and to estimate the feasibility of using the new POM/TiO2 cocatalyst in the photocatalytic degradation of 2,4-dichlorophenol (DCP) in aqueous media. Loading the PW12(3-) species on the surface of TiO2 enhances charge separation in the UV-illuminated TiO2, thereby accelerating the hydroxylation of the initial DCP substrate but not the mineralization of DCP, which is somewhat suppressed in the presence of the polyoxometalate. An increase in the load of POM increases the concentration of aromatic intermediates, and more toxic intermediates, such as 2,6-dichlorodibenzo-p-dioxin, 2,4,6-trichlorophenol, are detected in the PW12(3-)/TiO2 system. By contrast, cleavage of the whole conjugated structure of DCP predominates in TiO2 only dispersions. Strong ESR signals for the superoxide radical anionic species, O2*- (HO2* radicals in acidic media; pH < 5), are detected in TiO2 only dispersions; signals of O2*- are much weaker in the TiO2/ POM composite system under otherwise identical conditions. Experimental results infers that enhancement of charge separation in TiO2 photocatalysis does not always result in improvement of the efficiency of mineralization of organic substrates, and the reaction between organic radical cations and the formed superoxide radical anions may be responsible forthe mineralization of the chlorophenol.

This article examines the photoxidation of a dye (rhodamine‐B, RhB) by visible‐light irradiation in the presence of a polyoxometalate (12‐tungstosilicic acid, H4SiW12O40), and compares it with the analogous process in the presence of TiO2. The photoreaction processes were examined by UV‐visible spectroscopy, fluorescence spectroscopy, high‐performance liquid chromatography (HPLC), liquid chromatography/mass spectral techniques (LC‐MS), and total organic carbon (TOC) assays in order to identify the intermediates produced. Formation of oxygen species, such as H2O2 and O2.−, was also investigated to clarify the details of the reaction pathway. With the use of SiW12O404− ions as the photocatalyst, the photoreaction leads mainly to N‐dealkylation of the chromophore skeleton. In contrast, cleavage of the whole conjugated chromophore structure predominates in the presence of TiO2. Strong O2.−/HO2.− ESR signals were detected in the TiO2 dispersions, whereas only weak ESR signals for the O2.− radical ion were seen in the SiW12O404− solutions during the irradiation period. Experimental results imply that reduction of O2 occurs by different pathways in the two photocatalytic systems.

The dinuclear RuII-PdII complex shows efficient H2 production in the presence of triethylamine as a sacrificial electron and proton donor under visible light irradiation. XPS and TEM analyses reveal that photoreduction of PdII to Pd0 causes dissociation of Pd from the complex to form colloids that are suggested to be the actual catalyst for H2 production.

A Keggin polyoxometalate (POM, i.e., PW12O40(3-)) and its lacunary derivative are immobilized on an anionic exchange resin through electrostatic interaction at pH 4.6 in an aqueous dispersion. The resin-supported POM thus obtained catalyzes the efficient degradation of cationic dye pollutants in the presence of H2O2 under visible-light irradiation. To evaluate the photocatalytic system, degradation of a rhodamine B (RB) dye was investigated in detail using UV-visible spectroscopy, high performance liquid chromatography, and gas chromatography/mass spectrometry techniques to identify the intermediates and final products. Fluorescence lifetime measurements revealed the electron transfer from the visible-light-excited RB molecules to the POMs. Electron paramagnetic resonance measurements, investigation of the effects of *OH and *OOH scavengers on the photoreaction kinetics, and IR analysis indicated that de-ethylation of RB was due to *OOH radicals, but the decomposition of the conjugated xanthene structure was caused by the peroxo species formed by interaction of H2O2 with the lacunary POM loaded on the resin. A total organic carbon removal of ca. 22% was achieved, and the recycle experiment suggested excellent stability and reusability of the heterogeneous catalyst. On the basis of the experimental results, a photocatalytic mechanism is discussed.

Porous Co3O4/C nanocomposites derived from a Co-MOF exhibit an excellent electrochemical performance for high performance supercapacitors and the oxygen evolution reaction.

Metal sorption mechanisms were investigated for strontium, cobalt, and lead using sodium chloride, sodium nitrate, and sodium perchlorate as background electrolytes and quartz as the adsorbent. Spectroscopic analyses of concentrated sorption samples were evaluated for their ability to provide insight into the controlling sorption process for more dilute systems. For strontium, outer-sphere complexes identified using X-ray absorption spectroscopy (XAS) of concentrated samples were consistent with macroscopic sorption data collected in more dilute systems. XAS results indicated that cobalt formed a new solid phase upon sorption to silica. Macroscopic studies of cobalt sorption supported the spectroscopic data for total cobalt concentrations of 10(-5) M, regardless of the background electrolyte composition or concentration. At a lower total cobalt concentration (10(-7) M), adsorption appeared to be the prevailing mechanism of cobalt removal. Spectroscopic results suggested that lead adsorbed as an inner-sphere complex on silica. The decrease of lead removal with increasing chloride concentration was attributed to competition with aqueous lead-chloride complexes, based on thermodynamic calculations.

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Distinct from bulk materials, dealloyed nanoporous metals possess a large electrochemical surface area and abundant surface steps that are active for electrochemical reactions. Herein we fabricate a nanoporous gold electrocatalyst by electrochemical dealloying of potential cycling, which enables reducing carbon dioxide to carbon monoxide with a Faradaic efficiency of up to 98% at an overpotential of 390 mV. Pb-upd measurements verify that the high activity stems from the high density of step/kink sites with geometrically needed high-index facets on the curved internal surface. Moreover, a combination of X-ray photoelectron spectroscopy and in situ stripping voltammograms reveals that catalysis decay during long-term stability test results from the reduction of surface step/kink sites and the deposition of metal impurities (Zn, Pb, and Cu). The catalytic performance of the deactivated electrode can be recovered by applying potential cycling, which can restore the fractions of step/kink sites and remove surface metal impurities simultaneously.