Rational design and facile hydrothermal-thermal conversion synthesis of hierarchical porous urchin-like Cu_2-xSi₂O₅(OH)₃?xH_{2O and CuO/SiO2 hollow microspheres for high efficiency catalytic reduction of nitroarenes and adsorption of organic dye}

Hierarchical porous urchin-like Cu2-xSi2O5(OH)(3)center dot xH(2)O hollow microspheres constructed by radially aligned one-dimensional (1D) nanotubes (NTs) are rationally designed and facilely fabricated via a one-pot hydrothermal method (120 degrees C, 12.0 h) using abundant CuCl2 center dot 2H(2)O and Na2SiO3 center dot 9H(2)O as the basic raw materials, in the absence of any pre-prepared templates, additives or organic solvents. A probable etching formation mechanism of the Cu2-xSi2O5(OH)(3)center dot xH(2)O hollow microspheres assisted by the intermediate SiO2 nanospheres is proposed. The subsequent mild thermal conversion (750 degrees C, 2.0 h) results in CuO/SiO2 composite hollow microspheres. Both of the hierarchical porous Cu2-xSi2O5(OH)(3)center dot xH(2)O and CuO/SiO2 composite microspheres present highly catalytic activity to the reduction of the nitroarenes (e.g. 4-NP and 2-NP). Particularly, the hierarchical porous Cu2-xSi2O5(OH)(3)center dot xH(2)O hollow microspheres bearing high specific surface area (528.2 m2 g(-1)) and large pore volume (1.083 cm3 g(-1)) and in situ reduced highly dispersed metallic Cu-0 demonstrate high activity for the 4-NP reduction, with an exceptional rate constant (K-nor = 60.6 s(-1) g(-1)) higher than that of many other previously reported results. The synergic effect of the in situ reduced Cu0 and hierarchical porous structures on the reduction of 4-NP has also been deliberately investigated. Moreover, the Cu2-xSi2O5(OH)(3)center dot xH(2)O and CuO/SiO2 composite microspheres have also displayed excellent recycling catalytic performance during the tested 10 successive runs of reduction of 4-NP without significant degradation in its activity. Additionally, the Cu2-xSi2O5(OH)(3)center dot xH(2)O microspheres also exhibit excellent adsorption performance for removal of cationic dye methylene blue (MeB), with the maximum adsorption capacity q(m) of 242.5 mg g(-1). The hierarchical porous Cu2-xSi2O5(OH)(3)center dot xH(2)O and CuO/SiO2 composite microspheres thus demonstrate great potentials as low-cost, environmentally friendly and competitive candidates in future practical wastewater treatment.