Hydrothermal conversion (HTC), including hydrothermal liquefaction and hydrothermal carbonization, is a promising thermochemical technology for biomass utilization.

Sulfur-modified biochar was prepared and used to efficiently remove Chromium (Cr) from water. It was found that the sulfur-modified biochar prepared from lower primary pyrolysis temperature (400°C), appropriate secondary pyrolysis time, and S/C ratio was favorable for Cr removal. According to the response surface methodology analysis, the biochar prepared under the primary pyrolysis temperature of 350°C, secondary pyrolysis temperature of 450°C, secondary pyrolysis time of 60 min, and S/C ratio of 2:1 could achieve the maximum Cr removal (92%). The S-modified biochar prepared under the optimum condition exhibited greater capacity of adsorbing Cr(VI) or reducing Cr(VI) into Cr(III) compared with the biochar without the S modification. The enhanced Cr(VI) adsorption and reduction were likely because some of the sulfur-containing groups formed on the modified biochar could bind and interact with the Cr(VI). Besides, the enhanced surface area by the sulfur modification also played a role in prompting the removal and reduction of Cr(VI).

This study is committed to the synthesis and characterization of a series of bi-, tri- and tetranuclear coordination compounds. These compounds are produced through the reactions of zinc(II) or cadmium(II) ions as coordination centers with flexible bis(quinolyl) ligands HL1 (N,N′-bis-quinolin-2-ylmethylene-carbohydrazide) or HL2 (N,N′-bis-quinolin-2-ylmethylene-carbonothioic dihydrazide), in conjunction with chloride, thiocyanate, iodide or hydroxyl anions serving as the coordinated counterions. These compounds are denoted as [Zn₃(L1)₂Cl(NCS)₃]·2DMF·H₂O (1), [Zn₄(L1)₂Cl_3.8I_0.2(OH)₂]·8H₂O (2), [Cd₂(L1)I₃(H₂O)(DMF)]·DMF·0.25H₂O (3), [Zn₃(L2)₂Cl₄]·3DMF·2H₂O (4), [Zn₃(L2)₂Cl(NCS)₃]·3DMF (5), [Zn₄(L2)₂Cl₄(OH)₂]·3DMF·2H₂O (6), and [Cd₄(L2)₂I₆]·2DMF (7). An array of analytical techniques including elemental analyses, infrared (IR) spectroscopy, thermogravimetric (TG) analysis, powder X-ray diffraction (XRD) and comprehensive single crystal structure analyses have been utilized to elucidate the nature of these compounds. The crystal structures of compounds 1 to 7 exhibit complex supramolecular networks, arranged in zero, one, two, or three dimensions, primarily mediated by various interactions such as intermolecular π⋯π, C–H⋯π, C–H⋯Cl, and C–H⋯S weak interactions, in addition to hydrogen bonding. The structural diversity highlights the key roles of the variable coordinating counterions and the coordination modes of the iodide anions in shaping the architectures of the coordination compounds. Furthermore, the luminescence characteristics of compounds 1 to 7 have been assessed in the solid state.