Adsorption is a low-energy, economical, and efficient method for pollutant removal from water. Because of their unique structure, large specific surface area (SSA), and non-toxicity, bismuth-based semiconductors, usually researched for the photodegradation of organic molecules, are also excellent for dark adsorption processes. Here, a three-dimensional adsorbent with a heterostructure with a hydrangea-like shape made of Bi2MoO6(BMO) and BiOI (BOI) was synthesized by a one-pot solvothermal process and investigated for the adsorption of toxic dyes. BOI/BMO with an I-to-Mo ratio of 2.0 adsorbed 98.9% of the model pollutant rhodamine B (RhB) within 5 min with a maximum adsorption capacity of 72.72 mg/g in the dark at room temperature. When compared to pure BMO, the BOI2/BMO heterostructure was 14.1 times more performant because of its flower-like morphology with multiple planes, an SSA that was 1.6-fold larger, increased porosity, the formation of heterojunctions, and a negative surface charge attracting RhB. Further investigation indicated that adsorption by BOI2/BMO fitted the pseudo-second-order kinetic and the Langmuir isotherm models. In addition, the thermodynamic analysis showed that it was a spontaneous exothermic process probably relying on physisorption. Thus, the BOI/BMO adsorbent developed here is promising for the fast removal of toxic dyes from industrial wastewater.Keywords:BiOI/Bi2MoO6;heterostructure;rhodamine B;dark adsorption;kinetics;thermodynamic
In photocatalyst design, the rapid recombination of photo-generated electron–hole pairs in the bulk or on the surface of semiconductors is a major limiting factor in achieving high photocatalytic efficiency, which is a key scientific issue. Surface modification is used to change the surface properties of photocatalyst related to dark adsorption and photocatalytic efficiency. In this work, micro-sized CuO powder was surface modified by in situ-growing heterojunctions CuO/Cu 2 O and CuO/Cu 2 O/Cu when simply calcinating a mixture of CuO and urea, in which urea acted as a reducing agent. The phases, microstructure, composition, photogenerated carrier lifetime, dark adsorption rate, photodegradation rate, and surface charges of the as-modified powder were investigated. The surface modification was found to change the negative surface charge of micro-sized CuO to a positive one, resulting in enhanced dark adsorption (nearly twice that of pristine CuO). Furthermore, the surface modification prolonged the photogenerated carrier lifetime, which in turn enhanced the photocatalytic efficiency. Overall, this work implies that the electric properties of surface charges and carrier lifetime can be altered by constructing an appropriate heterojunction on the surface of the photocatalyst.
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