Substoichiometric titanium oxide Ti2O3 exhibits greater efficiency in enhancing hydrolysis of 1,1,2,2-tetrachloroethane than TiO2 nanomaterials.

Oxygen-deficient substoichiometric titanium oxides, or "titanium suboxides," are produced incidentally from coal combustion and are environmentally abundant. Additionally, titanium suboxide nanomaterials are promising new materials with likely future environmental release. How these materials may affect contaminant fate differently than stoichiometric TiO2 (nano)materials is largely unknown. Here, we show that Ti2O3 (selected as a model titanium suboxide) exhibits significantly greater efficiency in enhancing the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, than the stoichiometric anatase and rutile TiO2. At environmentally relevant pH (6.5-7.5), the surface area-normalized pseudo-first-order hydrolysis rate constant in the presence of Ti2O3 is approximately an order of magnitude higher than those associated with TiO2. The superior catalytic efficiency of Ti2O3 can be attributed to both its higher surface hydrophobicity, which renders higher adsorption affinity for TeCA, and its higher concentration of Lewis acid sites (mainly the Ti3+ and the five-coordinated Ti4+). Particularly, the deprotonated hydroxyl groups attached to Ti3+ (a weaker Lewis acid than Ti4+) exhibit higher basicity and thus, are more effective in catalyzing the base-promoted hydrolysis reaction. The findings call for further understanding of the environmental implications of titanium suboxide (nano)materials, which may not be readily predictable based on the knowledge acquired for TiO2.

Enhanced hydrolysis of 1,1,2,2-tetrachloroethane by multi-walled carbon nanotube/TiO2 nanocomposites: The synergistic effect.

Once released into the environment, engineered nanomaterials can significantly influence the transformation and fate of organic contaminants. To date, the abilities of composite nanomaterials to catalyze environmentally relevant abiotic transformation reactions of organic contaminants are largely unknown. Herein, we investigated the effects of two nanocomposites - consisting of anatase titanium dioxide (TiO2) with different predominantly exposed crystal facets (i.e., {101} or {001} facets) anchored to hydroxylated multi-walled carbon nanotubes (OH-MWCNT) - on the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, at ambient pH (6, 7 and 8). Both OH-MWCNT/TiO2 nanocomposites were more effective in catalyzing the dehydrochlorination of TeCA than the respective component materials (i.e., bare OH-MWCNT and bare TiO2). Moreover, the synergistic effect of the two components was evident, in that the incorporation of OH-MWCNT increased the TeCA adsorption capacity of the nanocomposites, significantly enhancing the catalytic effect of the deprotonated hydroxyl and carboxyl groups on nanocomposite surfaces, which served as the main catalytic sites for TeCA hydrolysis. The findings may have important implications for the understanding of the environmental implications of composite nanomaterials and may shed light on the design of high-performance nanocomposites for enhanced contaminant removal.

Fabrication of ternary reduced graphene oxide/SnS2/ZnFe2O4 composite for high visible-light photocatalytic activity and stability.

Metal sulfides are promising photocatalysts for efficient removal of organic pollutants in wastewater. However, the practical application of these catalysts is limited due to the fast recombination of charge carriers and poor catalyst stability. In this study, ternary reduced graphene oxide/SnS2/ZnFe2O4 (rGO/SnS2/ZnFe2O4) composites were synthesized by a hydrothermal process, and rGO content was optimized. The surface morphology, crystal structure, optical and electrochemical properties of rGO/SnS2/ZnFe2O4 composites were characterized. The adsorption capacity and visible-light photocatalytic activity of rGO/SnS2/ZnFe2O4 were influenced by rGO content with results revealing an optimal rGO content of 7wt.%. The 7% rGO/SnS2/ZnFe2O4 composite demonstrated the highest visible-light photocatalytic activity with almost 100% 2-nitrophenol removal, which could be attributed to the efficient charge separation, and the formation of O2-, h+ and a few OH radicals. The possible photocatalytic mechanism of rGO/SnS2/ZnFe2O4 composites was also provided based on the role of rGO and the energy bands of SnS2 and ZnFe2O4. Moreover, rGO/SnS2/ZnFe2O4 composites exhibit excellent reusability without an obvious decline in the photocatalytic activity after four degradation-regeneration cycles. The results indicate that ternary rGO/SnS2/ZnFe2O4 composites have good prospect in practical removal of organic pollutants in wastewater due to high efficiency and excellent stability.

Fabrication of 2D sheet-like BiOCl/carbon quantum dot hybrids via a template-free coprecipitation method and their tunable visible-light photocatalytic activities derived from different size distributions of carbon quantum dots.

A series of two-dimensional (2D) interlaced BiOCl/carbon quantum dot composites (denoted as BiOCl/CQD composites) were synthesized by a template-free coprecipitation method at room temperature, and the influence of different particle size distributions of the CQDs on the physiochemical properties and photocatalytic activities of the BiOCl/CQD composites was studied. CQDs can change the morphology and increase the specific surface area of the BiOCl/CQD composites. Moreover, the particle size distribution of the CQDs (CQD loading amount) has some effect on the light absorption, separation of photogenerated charge carriers, and photocatalytic performance of  the BiOCl/CQD composites. The optimized size distribution of the CQDs is 50-150 nm. BiOCl/CQD (50-150 nm) composites showed the best improvement of light absorption and the highest photocurrent density of 0.44 µA cm(-2), and exhibited the highest photocatalytic activity with almost 100% 2-nitrophenol removal under visible-light irradiation. The high efficacy of BiOCl/CQD (50-150 nm) composites could be attributed to their excellent light absorption and highly effective separation of photogenerated charge carriers.

Bio-inspired artificial functional photocatalyst: biomimetic enzyme-like TiO2/reduced graphene oxide nanocomposite with excellent molecular recognition ability.

An enzyme-like TiO(2)/reduced graphene oxide (enzyme-TiO(2)/rGO) nanocomposite with molecular recognition ability was fabricated by biomimicking the geometrical and chemical complementation of the enzyme and substrate. The anatase TiO(2) nanocrystals were densely dispersed on rGO nanosheets with close interfacial contacts. With geometrical and chemical matching of target molecules and memorized cavities, the adsorption capacity of enzyme-TiO(2)/rGO nanocomposites for 4-nitrophenol (4.71 mg g(-1)) is about six times that of control TiO(2)/rGO without the enzyme-like feature (0.79 mg g(-1)), and the enzyme-TiO(2)/rGO shows a relative selectivity coefficient of 7.24. Moreover, enzyme-TiO(2)/rGO exhibits molecular recognitive photocatalytic degradation for a particular contaminant. The results demonstrate that enzyme-substrate recognition provides a convenient and powerful basis on which to biomimic and construct efficient photocatalysts with high selectivity.