Efficient degradation of Rhodamine B in water by CoFe2O4/H2O2 and CoFe2O4/PMS systems: A comparative study.

In this work, a comparative study of efficient degradation of Rhodamine B (RhB) in CoFe2O4/H2O2 and CoFe2O4/PMS systems was performed. Batch experiments indicated that the RhB degradation rate of CoFe2O4/H2O2 system reached 95.5% at 90 min under the condition of 0.5 g L-1 of CoFe2O4 dosage, 10 mM of H2O2 concentration and 3.0 of initial pH. At certain conditions of initial pH = 7.0, 0.3 g L-1 of CoFe2O4 dosage, 7 mM of PMS concentration, CoFe2O4/PMS system could completely degrade RhB within 90 min. EPR and quenching experiments indicated that •OH was the main active species of CoFe2O4/H2O2 system, and •OH, SO4•-, •O2- and 1O2 participated in RhB degradation of CoFe2O4/PMS system. The circulate of Co(II)/Co(III) and Fe(II)/Fe(III) on the CoFe2O4 surface promoted the formation of free radical species in the two system. In CoFe2O4/PMS system, the formed •O2- and SO5•- realized the generation of non-free radical species (1O2). The LC-MS results indicated that N-de-ethylation, chromophore cleavage, opening rings and mineralization were the main steps for the RhB degradation of the two systems. After five cycles of degradation experiment, the CoFe2O4/H2O2 and CoFe2O4/PMS systems still maintained the high degradation rate (85.2% and 92.4%) and low mass loss (2.7% and 3.09%). In addition, CoFe2O4/PMS system had better potential value for the actual water and multi-pollutant degradation than CoFe2O4/H2O2 system. Finally, the toxicity analysis and cost assessment of the two oxidation systems were preliminarily evaluated.

Use of Eggshell-Catalyzed Biochar Adsorbents for Pb Removal from Aqueous Solution.

Eggshell is a cheap and environmentally friendly calcium source. In this study, Ca-modified biochar adsorbents (CEA) were prepared by 1:10, 1:2, and 1:1 mass ratio of the eggshell and Eupatorium adenophorum. The CEA-2 sample prepared with a 1:2 mass ratio showed a maximum Pb adsorption capacity (97.74 mg·g-1) at the conditions of an initial pH of 7.0, an adsorbent dosage of 0.5 g·L-1, and a contact time of 8.0 h. The kinetic and isotherm studies indicated that the adsorption process of the CEA-2 sample had monolayer adsorption characteristics, which was controlled together by intraparticle and interface diffusion. Thermodynamic studies indicated that the adsorption process of CEA-2 was spontaneous (ΔG 0 <0) and endothermic (ΔH 0 > 0). X-ray diffraction and scanning electron microscopy analyses showed a uniform distribution of Ca-Pb precipitation on the CEA-2 surface, which proved that chemical precipitation was the main adsorption mechanism. Fourier transform infrared spectra found that CEA-2 had abundant active groups, especially nitrogen-containing functional groups, which could adsorb Pb through a surface complexation reaction. The Brunauer-Emmett-Teller surface area of CEA-2 was found to be 621 m2·g-1, and such developed pores could ensure the smooth diffusion of Pb. Finally, the effect of coexisting cation and anion experiment and the cyclic regeneration experiment indicated that CEA-2 had prominent stability and reusability for Pb adsorption.