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Chemical pesticides and herbicides are one of the most important pollutants in urban, agricultural and industrial wastewaters. Improper discharge of these compounds into water bodies' cause harmful effects on both environment and human health. In this study, photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid (usually called 2,4-D) was investigated using Mn-doped zinc oxide/graphene nanocomposite under light emitting diodes (LED) radiation. FTIR, AFM, DLS, Zeta potential, XRD, and SEM techniques were used to determine the characteristics of the nanocomposite. The effects of process-related parameters, such as the amount of nanocomposite, initial pH, 2,4-D concentrations, and contact time, on the photocatalytic degradation of the 2,4-D were studied. The results showed that the efficiency of photocatalytic degradation of 2,4-D decreased with an increase in the initial concentration of 2,4-D, while photocatalytic degradation efficiency increased by increasing the initial pH and the nano-catalyst content. The results showed that 66.2% of 2,4-D could be photocatalytically degraded using Mn-doped zinc oxide/graphene nanocomposite under LED radiation at optimal conditions (pH 5, initial Zn concentration of 10 mg L−1, nano-composite concentration of 2 g L−1, contact time of 120 min). Findings of this experimental study concluded that photocatalysis using Mn-doped zinc oxide/graphene nanocomposite under LED radiation could efficiently remove 2,4-D herbicide from aqueous media. [ABSTRACT FROM AUTHOR]

The study is a first-time investigation into the use of Eucalyptus leaves as a low-cost herbal adsorbent for the removal of arsenic (As) and mercury (Hg) from aqueous solutions. The adsorption capacity and efficiency were studied under various operating conditions within the framework of response surface methodology (RSM) by implementing a four-factor, five-level Box-Wilson central composite design (CCD). A pH range of 3-9, contact time ( t) of 5-90 min, initial heavy metal (As or Hg) concentration ( C ) of 0.5-3.875 mg/L, and adsorbent dose ( m) of 0.5-2.5 g/L were studied for the optimization and modeling of the process. The adsorption mechanism and the relevant characteristic parameters were investigated by four two-parameter (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) isotherm models and four kinetic models (Lagergren's pseudo-first order (PFO), Ho and McKay's pseudo-second order (PSO), Weber-Morris intraparticle diffusion, and modified Freundlich). The new nonlinear regression-based empirical equations, which were derived within the scope of the study, showed that it might be possible to obtain a removal efficiency for As and Hg above 94% at the optimum conditions of the present process-related variables (pH = 6.0, t = 47.5 min, C = 2.75 mg/L, and m = 1.5 mg/L). Based on the Langmuir isotherm model, the maximum adsorption or uptake capacity of As and Hg was determined as 84.03 and 129.87 mg/g, respectively. The results of the kinetic modeling indicated that the adsorption kinetics of As and Hg were very well described by Lagergren's PFO kinetic model ( R = 0.978) and the modified Freundlich kinetic model ( R = 0.984), respectively. The findings of this study clearly concluded that the Persian Eucalyptus leaves demonstrated a higher performance compared to several other reported adsorbents used for the removal of heavy metals from the aqueous environment. [ABSTRACT FROM AUTHOR]

In the present study, multi-walled carbon nanotubes (MWCNTs) have been used for the rapid removal of four trihalomethanes (THMs) from aqueous solutions. The adsorption capacity of THMs onto MWCNTs was reasonably constant in the pH range of 5-7 but decreased as the pH exceeded 7. Four equilibrium isotherm models, namely, Langmuir, Freundlich, Temkin, and Sips, were applied to determine the best-fit equilibrium expressions. The results showed that all four experimental adsorption isotherms were best correlated by using the Sips model. The maximum adsorption capacities for the CHCl, CHClBr, CHClBr and CHBr were found to be 10.98, 6.85, 6.57, and 5.95 mg/g, respectively. The rate of adsorption followed the pseudo-second-order kinetic model. Furthermore, four nonlinear regression-based equations were also derived to model THM adsorption from aqueous solutions by MWCNTs. The modeling results clearly indicated that the empirical formulations satisfactorily described the behavior of the present adsorption process for CHCl ( R = 0.949), CHClBr ( R = 0.945), CHClBr ( R = 0.936), and CHBr ( R = 0.919). The overall results confirmed that MWCNTs could be a promising adsorbent material for THMs removal from aqueous solutions. [ABSTRACT FROM AUTHOR]