Biochar-supported magnesium oxide as high-efficient lead adsorbent with economical use of magnesium precursor.

With unique porous structure inherited from lignocellulose, biochar was an appropriate carrier for small-size MgO materials, which could simplify the synthetic process and better solve agglomeration and separation problems during adsorption. Biochar-supported MgO was prepared with impregnation method. Under different synthesis conditions, the obtained MgO presented diverse properties, and moderate pyrolysis condition was conducive to the improvement of Mg conversion rate. The Pb(II) capacity was highly correlated with Mg content, rather than the specific surface area. Reducing the pyrolysis temperature or increasing the usage of supporter could improve adsorption efficiency when using Mg content-normalized capacity as the criterion. The better release ability of Mg, contribute by the higher extent of hydration and better spread of MgO, were the critical factors. The maximal Mg content-normalized capacity could reach 0.932 mmol·mmol-Mg-1 with the mass ratio of biochar/MgCl2·6H2O = 4:1 at the pyrolysis temperature of 600 °C. Considering the ultimate utilization efficiency of Mg in precursor, the optimum Mg consumption-normalized capacity was 0.744 mmol·mmol-Mg-1 with the mass ratio of biochar/MgCl2·6H2O = 1:1 at 600 °C.

Influence of adsorption sites of biochar on its adsorption performance for sulfamethoxazole.

In this study, the effects of various types of key adsorption sites on biochar were investigated on its adsorption capacity for sulfamethoxazole (SMX). The biochar obtained by carbonization of corncob at 800 °C (named CC800) was applied to the adsorption of SMX in aqueous environment. The adsorption of SMX by CC800 exhibited a "Three-stage downward adsorption ladder" characteristic in the whole pH range, which was attributed to the different mechanisms corresponding to different adsorption sites of CC800. The organic solvent method and heat treatment method restored the adsorption sites of CC800 after saturated adsorption. And the results revealed that the pore structure and aromatic structure under acidic conditions, and surface functional groups and pore structure under alkaline conditions were confirmed to be key SMX adsorption sites. The adsorption energies of each adsorption mechanism were calculated by density functional theory (DFT), and their order was (-)CAHB (-COO-) > π+-π EDA interaction > (-)CAHB (-O-) > pore filling mechanism > π-π EDA interaction. Based on the above studies, the adsorption performance of biochar to SMX can be improved by targeted modification of its micropore structure, surface functional groups, and aromatic structures.

Preparation of nitrogen doped magnesium oxide modified biochar and its sorption efficiency of lead ions in aqueous solution.

A N-doped couping MgO-modified biochar (MgO-N-BC) was synthesized from corncob-to-xylose residue by two-step slow pyrolysis method. The biochar exhibited a remarkable Pb(II) sorption capacity (maximum 1429 mg·g-1) in aqueous solution. The sorption of Pb(II) onto MgO-N-BC best fitted Freundlich model and pseudo-second-order equation. Further analysis demonstrated the final product of Pb were mainly hexagonal crystal hydrocerussite flakes. The combine of ion-exchange and precipitation process play key role in the sorption of Pb(II), while interactions between Pb(II) and functional groups work, too. The sorption capacity decreased by 63.5% with CO2 free, however over supply of CO2 effects little on the sorption capacity while that can shorten equilibrium time from near 360 min to about 30 min. Only few co-existing ions such as Ba2+ and Fe3+ can decrease the sorption partly, and NH4+ block the sorption obviously, while Mg2+ had an enhancement effect.