Simultaneous reduction of copper and toxicity in semiconductor wastewater using protonated alginate beads

Using protonated alginate (HA) beads, copper (Cu2+) levels and toxicity were concurrently reduced in semiconductor wastewater produced from the chemical mechanical planarization process. The beneficial effect of protonation could be explained by a reduction in the release of Ca2+, which is a competitive cation during sorption of Cu2+, leading to an increased in the sorption capacity from 107 to 189 mg/g. Monitoring of the acute toxicity of two different types of semiconductor wastewater toward Daphnia magna suggested that Cu2+ was the cause of toxicity. The toxicity identification evaluation using D. magna indicated that Cu2+ was a major toxicant in the raw wastewater with concentrations of 1.97 and 3.37 mg/L for two different raw wastewater samples with initial toxicities of 14.2 and 23.6 toxic unit (TU), respectively. This relationship was verified by the correlation coefficients between Cu2+ concentration and acute toxicity (r(2) = 0.829 at P < 0.05 and 0.894 at P < 0.05 for two types of semiconductor wastewater) in mass balance tests. The laboratory continuous column test using HA beads showed that the Cu2+ concentration in effluent was proportional to the acute toxicity. In particular, the TU values increased sharply when the residual concentration of Cu2+ exceeded 0.1 mg/L. The test battery results indicated that D. magna was more sensitive than other aquatic species, i.e., algae and bacteria, to Cu2+ in semiconductor wastewater. (C) 2015 Elsevier B.V. All rights reserved.1110Nsciescopu

Gas-Phase Alkali Metal-Assisted MOCVD Growth of 2D Transition Metal Dichalcogenides for Large-Scale Precise Nucleation Control

Advances in large-area and high-quality 2D transition metal dichalcogenides (TMDCs) growth are essential for semiconductor applications. Here, the gas-phase alkali metal-assisted metal-organic chemical vapor deposition (GAA-MOCVD) of 2D TMDCs is reported. It is determined that sodium propionate (SP) is an ideal gas-phase alkali-metal additive for nucleation control in the MOCVD of 2D TMDCs. The grain size of MoS2 in the GAA-MOCVD process is larger than that in the conventional MOCVD process. This method can be applied to the growth of various TMDCs (MoS2, MoSe2, WSe2, and WSe2) and the generation of large-scale continuous films. Furthermore, the growth behaviors of MoS2 under different SP and oxygen injection time conditions are systematically investigated to determine the effects of SP and oxygen on nucleation control in the GAA-MOCVD process. It is found that the combination of SP and oxygen increases the grain size and nucleation suppression of MoS2. Thus, the GAA-MOCVD with a precise and controllable supply of a gas-phase alkali metal and oxygen allows achievement of optimum growth conditions that maximizes the grain size of MoS2. It is expected that GAA-MOCVD can provide a way for batch fabrication of large-scale atomically thin electronic devices based on 2D semiconductors