Tuning sol size to optimize organosilica membranes for gas separation

A series of organosilica sols are prepared by the polymeric sol–gel method using 1,2-bis(triethoxysilyl)ethane(BTESE)as the precursor.Particle size distributions of the BTESE-derived sols are systematically investigated by carefully adjusting the synthesis parameters(i.e.,water ratios,acid ratios and solvent ratios)in the sol process.In certain conditions,increasing the water ratio or the acid ratio tends to cause larger sol sizes and bimodal particle size distributions.However,higher solvent ratios lead to smaller sol sizes and unimodal particle size distributions.The organosilica membranes prepared from the optimized sols show excellent H_2 permeances(up to 4.2×10^(-7)mol·m^(-2)·s^(-1)·Pa^(-1))and gas permselectitivies(H_2/CO_2 is 9.5,H_2/N_2 is 50 and H_2/CH_4 is 68).This study offers significant insights into the relationship between the sol synthesis parameters,sol sizes and membrane performance.

Negatively charged organic–inorganic hybrid silica nanofiltration membranes for lithium extraction

Effective extraction of lithium from high Mg2+/Li+ratio brine lakes is of great challenge.In this work,organic–inorganic hybrid silica nanofiltration(NF)membranes were prepared by dip-coating a 1,2-bis(triethoxysilyl)ethane(BTESE)-derived separation layer on tubular TiO2 support,for efficient separation of LiC l and MgCl2 salt solutions.We found that the membrane calcinated at 400°C(M1–400)could exhibit a narrow pore size distribution(0.63–1.66 nm)owing to the dehydroxylation and the thermal degradation of the organic bridge groups.All as-prepared membranes exhibited higher rejections to LiCl than to MgCl2,which was attributed to the negative charge of the membrane surfaces.The rejection for LiCl and MgCl2 followed the order:LiCl N MgCl2,revealing that Donnan exclusion effect dominated the salt rejection mechanism.In addition,the triplecoated membrane calcined at 400°C(M3–400)exhibited a permeability of about 9.5 L·m-2·h-1·bar-1 for LiCl or MgCl2 solutions,with rejections of 74.7%and 20.3%to LiCl and MgCl2,respectively,under the transmembrane pressure at 6 bar.Compared with the previously reported performance of NF membranes for Mg2+/Li+separation,the overall performance of M3–400 is highly competitive.Therefore,this work may provide new insight into designing robust silica-based ceramic NF membranes with negative charge for efficient lithium extraction from salt lakes.

Direct Colorimetric Detection of Hydrogen Peroxide Using 4-Nitrophenyl Boronic Acid or Its Pinacol Ester

A colorimetric method for the direct determination of hydrogen peroxide in aqueous solution is described. H2O2 stoichiometrically converts 4-nitrophenyl boronic acid or 4-nitrophenyl boronic acid pinacol ester into 4-nitrophenol, which can be quantified by measuring the absorption at 400 nm in neutral or basic media. The reactions proceed fast under basic conditions and complete in 2 minutes to at pH 11 and 80?C. The linear range for the colorimetric method extends beyond 1.0 to 40 μM H2O2, and the limit of detection is ~1.0 μM H2O2. This method offers a convenient and practical process for rapid determination of hydrogen peroxide in aqueous media. Compared to many other techniques in H2O2 detection, this process is a direct measurement of H2O2, and is relatively unaffected by the presence of various salts, metal ions and the chelator EDTA.

Fabrication of Pd-Nb bimetallic doped organosilica membranes by different metal doping routes for H_(2)/CO_(2) separation

Monometallic doping has proved its superiority in improving either permselectivity or H_(2) permeability of organosilica membranes for H_(2)/CO_(2) separation,but it is still challenging to break the trade-off effect.Herein,we report a series of Pd-Nb bimetallic doped 1,2-bis(triethoxysilyl)ethane(Pd-Nb-BTESE,PNB)membranes with different metal doping routes for simultaneously improving H_(2) permeance and H_(2)/CO_(2) permselectivity by the synergetic effects of Pd and Nb.The doped Pd can exist in the BTESE network as nanoparticles while the doped Nb is incorporated into BTESE network forming Nb-O-Si covalent bonds.The metal doping routes significantly influence the microstructure of PNB networks and gas separation performance of the PNB membranes.We found that the PNB membrane with Pd doping priority(PNB-Pd)exhibited the highest surface area and pore volume,comparing with Nb doping priority(PNB-Nb)or Pd-Nb simultaneous doping(PNB-PdNb).The PNB-Pd membrane could not only exhibit an excellent H_(2) permeance of~10^(−6) mol·m^(−2)·s^(−1)·Pa^(−1) but also a high H_(2)/CO_(2) permselectivity of 17.2.Our findings may provide novel insights into preparation of bimetallic doped organosilica membranes with excellent H_(2)/CO_(2) separation performance.