Liqin Cao

Characterization and adsorptive properties of poly(1-vinylimidazole)/silica nanocomposites synthesized in supercritical carbon dioxide

Abstract Poly(1-vinylimidazole) (PVIm)/silica nanocomposite particles were prepared via free radical polymerization of VIm in the presence of unmodified silica and crosslinker N,N′-methylenebisacrylamide without any surfactant by a one-pot route in supercritical carbon dioxide. The strong acid-base interaction between the hydroxyl groups (acidic) of silica surfaces and the imidazole groups (basic) of 1-VIm was strong enough to promote the formation of long-stable PVIm/silica nanocomposite particles. Transmission electron microscopy and scanning electron microscopy results showed that the silica nanoparticles were encapsulated into the polymer and with a specific pore structure. Fourier transform infrared spectroscopy results suggested the strong interaction between PVIm and silica. The nanocomposites were shown to possess higher thermal stability than PVIm. A maximum surface area of 60.76 m2/g was obtained via standard nitrogen adsorption analysis. The property of the composite materials in terms of heavy metal ion removal was investigated. The maximum adsorption capacity of Cr (VI) is 331.5 mg/g in the experimental range.

Characterization and adsorption performance of chitosan/diatomite membranes for Orange G removal

Abstract Novel chitosan/diatomite (CS/DM) membranes were prepared by phase inversion technique to remove anionic azo dyes from wastewater. The fabricated composite membranes exhibited the combined advantages of inorganic substances, diatomites, and polysaccharides. These composite membranes were characterized through Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. The mechanical properties of the membranes were also evaluated. Adsorption experiments were conducted under varied initial dye concentration, solution pH values, contact time, and adsorbent dosage. The results indicate that pH 3 is the optimal pH value for Orange G adsorption. The CS/DM membranes exhibit the highest adsorption capacity of 588 mg g-1 and removal rate of 94% under an initial dye concentration of 200 mg l-1, contact time of 6 h, and membrane dosage of 8 mg. Langmuir, Freundlich and Redlich-Peterson adsorption models were applied to describe the equilibrium isotherms at different dye concentrations. The equilibrium data was found to be fitted well to the Redlich-Peterson isotherm. Pseudo-first-order and pseudo-second-order kinetics models were used to describe the adsorption of membranes. The adsorption data were well explained by pseudo-second-order models, and also followed by the Elovich model. In addition, these membranes display high adsorption capacity and mechanical performance even after reused for seven times.

Facile preparation of UiO-66 /PAM monoliths via CO2-in-water HIPEs and their applications

A novel clean method to synthesis a composite monolith was developed. Given its amphiphilic property, UiO-66 can emulsify water and CO2 to format a high internal phase emulsion (HIPE) under certain conditions. These UiO-66-emulsified Pickering HIPEs can be used as templates to prepare interconnected macroporous MOF/polymer composite monoliths. The effects of UiO-66 amount, cross-linking agent concentration, and CO2–water ratio on UiO-66/PAM structures were investigated. Then, the as-synthesized MOF/PAM composites were characterized by TGA, XRD, SEM, and FT-IR analyses, as well as rheological and DMA measurements. The results indicated that the composites are interconnected with hierarchical pores, and the diameter of the voids is 10–50 μm. The directly prepared monoliths exhibited relatively high stresses at 82% strain and recovered their shape quickly. The adsorption capacity of the composites for methylene blue (MB) is 50 mg g−1 at a faster adsorption rate. The monoliths also exhibit underlying applications in edible oil–water separation.

Preparation of PHEMA/nHAP nanocomposites via in situ polymerization in supercritical carbon dioxide for biomedical applications

Poly(2-hydroxyethylmethacrylate) (PHEMA)/hydroxyapatite (HAP) nanocomposites were synthesized through a new route involving nano-sized HAP (nHAP) particles or modified nHAP mixed with monomer 2-hydroxyethylmethacrylate via in situ polymerization in supercritical carbon dioxide (scCO2). Fourier-transform infrared spectroscopy showed phosphate peak increased with nHAP content in composite. X-ray diffraction patterns of PHEMA/nHAP revealed the presence of crystallized nHAP. Thermogravimetric analysis showed that the ultimate nHAP content in PHEMA/nHAP composites is consistent with its initial amount. Scanning electron microscopy revealed that nanocomposite particles are much smaller than PHEMA particles. PHEMA/nHAP composites with average diameter of approximately 600 nm were obtained in scCO2 with 94 % yield. Mechanical properties of PHEMA/nHAP nanocomposites were better than those of PHEMA, and compressive modulus and strength of composites with 30 wt.% nHAP were 193 and 29 MPa, respectively. Nanocomposite adsorption toward bovine serum albumin was evaluated, and results indicated that analyte adsorption amount can reach up to 282 mg/g.

Grafting of thermo- and pH-responsive polymer inside mesoporous silica foam in supercritical carbon dioxide for controlled release of 5-fluorouracil

Mesocellular silica foam (MCF) grafted with thermo-responsive and pH-responsive copolymer poly(N-isopropylacrylamide-co-acrylic acid), was prepared by precipitation polymerization using supercritical carbon dioxide (scCO2) as entrainer and solvent. Vinyl-functionalized MCF was first synthesized through post-synthesis via using vinyltriethoxysilane as a coupling agent for surface modification. Entrapped monomers of N-isopropylacrylamide (NIPA) and acrylic acid (AA) were then introduced and assembled onto the vinyl-modified MCF with the aid of scCO2. The grafting copolymer performed here as an on/off switch in the release of 5-fluorouracil, as confirmed by using UV-visible absorption spectroscopy. The grafted organic content and drug loading efficiency were 65.2 wt% and 11.5 wt%, respectively. The resultant grafting composite showed potential for application in drug delivery and exhibited thermo- and pH-responsiveness to external environmental changes.

Characterization and adsorptive properties of cross-linked poly (1-vinylimidazole)-iron (III) complex synthesized in supercritical carbon dioxide

Abstract In this study, poly (1-vinylimidazole)-iron(III) [PVIm-Fe(III)] complex was investigated along with adsorption behavior of bovine serum albumin (BSA). The cross-linked PVIm-Fe(III) was synthesized in supercritical carbon dioxide by using N,N′-methylenebisacrylamide (BIS) as a cross-linker. The obtained products were analyzed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) analysis. The results reveal that iron ion is complexed by coordination with basic (-N) functional groups of 1-vinylimidazole successfully. The effects of the operating pressure, the ratio of iron and cross-linker concentration were investigated. A fine and yellow powder was obtained at high yield and crosslinking degrees at 20 MPa, 70°C. Additionally, the property of PVIm-Fe(III) complexes in terms of BSA adsorption has been studied, and the higher adsorption capacity was 660 mg/g.