1,10-Dichlorodecane (D 2 C 10 ) is shown to be effectively photodegraded in aqueous suspensions of TiO 2 using a photoreactor equipped with 300 nm lamps. Solutions exposed to UV light intensities of 3.6 × 10 -5 Ein L -1 min -1 , established by ferrioxalate actinometry, showed negligible direct photolysis in the absence of TiO 2 . The degradation rate was optimal with 150 mg/L of TiO 2 and a D 2 C 10 concentration (240 µg/L) approaching its solubility limit. Kinetics of photodegradation followed a LangmuirHinshelwood model suggesting that the reaction occurred on the surface of the photocatalyst. The presence of h + vb and OH • radical scavengers, including methanol and iodide, inhibited the degradation supporting a photooxidation reaction. Electron scavengers (Ag + , Cu 2+ , and Fe 3+ ) had small effects on the degradation rate. The lack of transformation of D 2 C 10 in acetonitrile as solvent indicated that the major oxidants were OH • radicals. The presence of tetranitromethane, effectively eliminating the formation of free OH • radicals, did not affect the degradation rates significantly. This result, combined with observed increases in photolysis rates with the degree of adsorption of D 2 C 10 onto the surface of the photocatalyst, confirmed that the reaction involved adsorbed 1,10-dichlorodecane and surface bound OH • radicals.
In this research miswak leaves, agriculture wastes, available in large quantity in Saudi Arabia, was used as low-cost adsorbent for removing methylene blue (MB) dye. Equilibrium behavior of miswak leaves was investigated by performing batch adsorption experiments. The effects of [MB] 0, pH, contact time and adsorbent dose were evaluated. An alkaline pH (10.6) was favorable to the adsorption of MB dye. Adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. Langmuir equation was found to have the highest value of R2 compared with other models. Furthermore, it was found that miswak leaves have a high adsorptive capacity towards MB dye (200 mg/g) and show favorable adsorption of MB dye with separation factor (R<sub>L</sub> < 1). In addition, pseudo-first- order, pseudo-second order and intra-particle diffusion were used to study the kinetics of MB adsorption onto miswak leaves. Adsorption process undergoes pseudo-second order kinetic as proved by the high value of R2 and the low value of sum of squared error (SSE percentage). Results indicated that intra-particle diffusion is not the limiting step, and the adsorption process is spontaneous as indicated by the negative value of the
This research aims to use modified ZnO nanoparticles to enhance the removal rate of the methylene blue (MB) dye. ZnO nanoparticles are modified by coating their surface with Congo red (CR) dye, henceforth referred to as ZnO/CR. This process is used to produce a Lewis acid on the surface of ZnO to attract any Lewis base such as a MB dye (MB+). Therefore, the stability of ZnO/CR improved, and it resists the change in pH value (from 3 to 9). Several analysis techniques such as scanning electron microscopy, X-ray diffraction, FTIR, and BET method were used to characterize ZnO/CR. Nonlinear and linear regressions of pseudo first-order, pseudo second-order, and Elovich models were used to calculate the kinetic parameters of the adsorption process. The best-fit kinetic equation was investigated using three functions of error analysis: the sum of the squares of the errors, chi-square analysis, and the coefficient of determination. The intraparticle diffusion equation was used to study the diffusion process. The adsorption process of the MB followed the Langmuir model with a maximum capacity (qm) value of 43.5 mg/g. This value is six times greater than the value calculated with pure ZnO. Thermodynamic parameters ΔS•, ΔH•, and ΔG• were investigated at four temperatures (10, 20, 30, and 40 °C). The uptake process of the MB occurs spontaneously following endothermic process and an increase in the system disorder. The rate of adsorption was controlled mainly by a Lewis acid–base interaction and H bonding. Furthermore, the removal of the MB by ZnO/CR powder worked well as a chemical and physical adsorption process.
In this research dobera leaves (DL), an agricultural waste, available in large quantity in south region of Saudi Arabia, were used as low-cost adsorbent for removal of metal ions such as Pb(II). Batch operation was used to study the equilibrium behavior of DL. The effects of initial concentration of Pb(II), solution pH, contact time and adsorbent dose were evaluated. To study the kinetics of adsorption of Pb(II) onto DL, pseudo-first-order, pseudo-second-order and intra-particle diffusion were used. Adsorption process undergoes pseudo-second-order kinetic as proved by the high value of R 2. Furthermore, to design the equilibrium data of adsorption of process, four adsorption isotherm models such as Langmuir, Freundlich Temkin and Dubinin-Radushkevich (D-R) were used. It is found that Langmuir equation has the highest value of R 2 (0.999) compared with other models. In presences of a mixture of Pb(II)/Ni(II), DL were found to be selective for Pb(II) ions with a high adsorptive capacity of 83 mg/g and show favorable adsorption with RL < 1. In addition, preliminary results indicate that DL are very effective adsorbent for the removal of Pb(II) ions (>90%) from drinking water with less competition of other ions present in water.
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