Maolin Zhai

Syntheses of PVA/starch grafted hydrogels by irradiation

A series of excellent polyvinyl alcohol (PVA)/starch blend hydrogels were prepared by gamma and electron beam radiation at room temperature. The influence of dose, the content of starch in blend systems on the properties of the prepared hydrogels was investigated. The gel strength was improved obviously after adding starch into PVA hydrogels, but the swelling properties decreased slightly due to poor hydrophilicity of starch. In order to elucidate the effect of component of starch on the properties of PVA/starch hydrogels as well as the formation mechanism of PVA/starch blend hydrogels under irradiation, the two components of starch, amylose and amylopectin, were chosen to blend with PVA to prepare the hydrogels, respectively. The results indicated that the amylose of starch was a key component that influenced the properties of PVA/starch blend hydrogels. The further analyses of FTIR, DSC and TGA spectra of the prepared gels after extracting sol manifested that there was a grafting reaction between PVA and starch molecules besides the crosslinking of PVA molecules under irradiation, and the amylose of starch was a key reactive component.

Synthesis of antibacterial PVA/CM-chitosan blend hydrogels with electron beam irradiation

A series of excellent hydrogels were prepared from poly(vinyl alcohol) (PVA) and carboxymethylated chitosan (CM-chitosan) with electron beam irradiation (EB) at room temperature. Electron spectroscopy analysis of the blend hydrogels revealed that good miscibility was sustained between CM-chitosan and PVA. The properties of the prepared hydrogels, such as the mechanical properties, gel fraction and swelling behavior were investigated. The mechanical properties and equilibrium degree of swelling improved obviously after adding CM-chitosan into PVA hydrogels. The gel fraction determined gravimetrically showed that a part of CM-chitosan was immobilized onto PVA hydrogel. The further analyses of FTIR and DSC spectra of the prepared gels after extracting sol manifested that there was a grafting interaction between PVA and CM-chitosan molecules under irradiation. The antibacterial activity of the hydrogels against Escherichia coli was also measured via optical density method. The blend hydrogels exhibited satisfying antibacterial activity against E. coli, even when the CM-chitosan concentration was only 3 wt%.

Facile synthesis of well-dispersed graphene by γ-ray induced reduction of graphene oxide

We demonstrate a facile and environmentally friendly approach to prepare well-dispersed graphene sheets by γ-ray induced reduction of a graphene oxide (GO) suspension in N,N-dimethyl formamide (DMF) at room temperature. GO is reduced by the electrons generated from the radiolysis of DMF under γ-ray irradiation. The reduced GO by γ-ray irradiation (G-RGO) can be re-dispersed in many organic solvents, and the resulting suspensions are stable for two weeks due to the stabilization of N(CH3)2+ groups on G-RGO. Additionally, G-RGO is efficient in improving the conductivity of polystyrene (PS). Its PS nanocomposites exhibit a sharp transition from electrically insulating to conducting with a low percolation threshold of 0.24 vol% and a high electrical conductivity of 45 S m−1 is obtained with only 2.3 vol% of G-RGO. The superior electrical conductivity is attributed to the uniform dispersion of the G-RGO sheets in the PS matrix.

Radiation modification of starch-based plastic sheets

Transparent starch-based plastic sheets were prepared by irradiation of compression-molded starch-based mixture in physical gel state with electron beam (EB) at room temperature. The influence of radiation, plasticizers, water and poly vinyl alcohol (PVA) on the properties of the sheets was investigated. After irradiation, the ductility and tensile strength of the sheets was improved due to the chemical reactions, which was demonstrated by determination of gel fraction and DSC profiles, between starch macromolecules under the action of ionizing radiation. Glycerol, ethylene glycol (EG), poly ethylene glycol (PEG, 600, 1000) was selected as plasticizer to add into starch sheets. The results showed that glycerol was an excellent plasticizer of starch so that the ductility of starch sheets was improved obviously (elongation at break increased). The presence of water was necessary for the preparation of the sheets in this work. With the increasing of the content of starch in starch-based mixture, the tensile strength of the sheets decreased due to the decrease of the degree of the crosslinking of starch. Furthermore, PVA, a biodegradable and flexible-chain polymer, was incorporated into starch-based sheets, the properties of the sheets such as the flexibility (elongation at break) and wet strength was improved obviously.

Radiation preparation and swelling behavior of sodium carboxymethyl cellulose hydrogels

Sodium carboxymethyl cellulose (CMC) is a kind of degraded polymer under γ-irradiation. However, in this work, it has been found that CMC crosslinks partially to form hydrogel by radiation technique at more than 20% CMC aqueous solution. The gel fraction increases with the dose. The crosslinking reaction of CMC is promoted in the presence of N2 or N2O due to the increase of free radicals on CMC backbone, but gel fraction of CMC hydrogel is not high (<40%). Some important values related to this kind of new CMC hydrogel synthesized under different conditions, such as radiation yield of crosslinking G(x), gelation dose Rg, number average molecular weight of network Mc were calculated according to the Charlesby–Pinner equation. The results indicated that although crosslinked CMC hydrogel could be prepared by radiation method, the rate of radiation degradation of CMC was faster than that of radiation crosslinking due to the character of CMC itself. Swelling dynamics of CMC hydrogel and its swelling behavior at different conditions, such as acidic, basic, inorganic salt as well as temperature were also investigated. Strong acidity, strong basicity, small amount of inorganic salts and lower temperature can reduce swelling ratio.

Adsorption of Cr(VI) using silica-based adsorbent prepared by radiation-induced grafting

Silica-based adsorbent was prepared by radiation-induced grafting of dimethylaminoethyl methacrylate (DMAEMA) onto the silanized silica followed by a protonation process. The FTIR spectra and XPS analysis proved that DMAEMA was grafted successfully onto the silica surface. The resultant adsorbent manifested a high ion exchange capacity (IEC) of ca. 1.30 mmol/g and the Cr(VI) adsorption behavior of the adsorbent was further investigated, revealing the recovery of Cr(VI) increased with the adsorbent feed and the equilibrium adsorption could be achieved within 40 min. The adsorption capacity, strongly depended on the pH of the solution, reached a maximum Cr(VI) uptake (ca. 68 mg/g) as the pH was in the range of 2.5-5.0. Furthermore, even in strong acidic (4.0 mol/L HNO(3)) or alkaline media (pH 11.0), the adsorbent had a sound Cr(VI) uptake capacity (ca. 22 and 30 mg/g, respectively), and the adsorption followed Langmuir mode. The results indicated that this adsorbent, prepared via a convenient approach, is applicable for removing heavy-metal-ion pollutants (e.g. Cr(VI)) from waste waters.

Adsorption and desorption of Sr(II) ions in the gels based on polysaccharide derivates

Adsorption behavior of Sr(II) ions was investigated using gel adsorbents based on three types of polysaccharide derivates: carboxymethylated cellulose (CMC), carboxymethylated chitosan (CMCts) and hydroxypropyl methylcellulose phthalate (HPMCP). Maximum adsorption capacities were reached in about 0.5h for CMCts, 1h for CMC, and 2h for HPMCP. The adsorption capacity increased with increasing pH, and decreasing ionic strength. The maximum adsorption capacity of Sr(II) ions into CMC, CMCts and HPMCP gels at 25 degrees C were 108.7, 99.0, and 83.3mg/g gel, respectively, based on the Langmuir isotherms. XPS analysis indicates that Sr(II) ions are adsorbed into the three adsorbents according to the ion-exchange mechanism. Desorption of Sr(II) ions could be carried on by immersing the adsorbents in the solutions with low pH or high ionic strength, or heating the adsorbents in the moist hot environment.

Radiation Effects on Hydrophobic Ionic Liquid (C4mim)(NTf2) during Extraction of Strontium Ions

The applications of room-temperature ionic liquids (RTILs) in separation of high level radioactive nuclides demand a comprehensive knowledge of the stability and metal ion extraction of RTILs under radiation. Herein, we assessed the influence of gamma-irradiation on the [C(4)mim][NTf(2)]-based extraction system, where [C(4)mim](+) is 1-butyl-3-methylimidazolium and [NTf(2)](-) is bis(trifluoromethylsulfonyl)imide, by solvent extraction of Sr(2+) using irradiated [C(4)mim][NTf(2)] in combination with dicyclohexyl-18-crown-6 (DCH18C6). It was found that the degree of extraction for Sr(2+) from water to irradiated [C(4)mim][NTf(2)] decreased compared with that to unirradiated [C(4)mim][NTf(2)], and the decrement enhanced obviously with increasing dose. NMR spectroscopic probe analysis revealed the formation of acids during irradiation of [C(4)mim][NTf(2)]. The decrease of Sr(2+) partitioning in irradiated [C(4)mim][NTf(2)] is attributed to the competition between H(+) with Sr(2+) to interact with DCH18C6. Accordingly, washing irradiated [C(4)mim][NTf(2)] with water gives a simple way of ionic liquid recycling. Furthermore, the degree of extraction for Sr(2+) from 3 mol.L(-1) nitric acid solution to [C(4)mim][NTf(2)] is independent of the irradiation of [C(4)mim][NTf(2)] since the amount of the radiation-generated H(+) is negligible in such a high acidic solution.

Selective adsorption of Hg(II) by γ-radiation synthesized silica-graft-vinyl imidazole adsorbent

Silica-based adsorbent was prepared by γ-radiation induced grafting of vinyl imidazole (VIM) onto the silanized silica, which was silanized by chlorotrimethylsilane (TMCS). The effects of monomer concentration and absorbed dose on the grafting yield were investigated to optimize the reaction conditions. Thermodynamic analysis, FTIR analysis and XPS spectra manifested that VIM was successfully grafted onto the silica surface. The SS-g-VIM adsorbent had excellent selectivity for Hg(II) adsorption in mixture divalent cationic metal solution and a high adsorption capacity of Hg(II). The theoretical maximum adsorption capacity was calculated to be 355.9 mg g(-1) (1.774 mmol g(-1)) in HgCl(2)/HNO(3) solution at pH 5 at room temperature. The adsorption kinetics and adsorption isotherm were investigated. It was found that the Langmuir isotherm model fitted well with the adsorption process and the adsorption of Hg(II) onto SS-g-VIM adsorbent could be considered as a spontaneous, endothermic and chemical sorption process. The comprehensive results suggested that SS-g-VIM adsorbent has potential application for the removal of Hg(II) from wastewater.

A facile synthesis of platinum nanoparticle decorated graphene by one-step γ-ray induced reduction for high rate supercapacitors

A facile method has been developed to synthesize a high-quality platinum nanoparticle (PtNP) decorated graphene via one-step γ-ray induced reduction of graphite oxide (GO) and chloroplatinic acid at room temperature. GO and Pt(IV) precursor salt could be co-reduced by the electrons generated from the radiolysis of ethylene glycol under γ-ray irradiation. The synchronous reduction of the metal precursor and regulation of pH greatly increased the ratio of C/O in the reduced GO (RGO). PtNPs with an average diameter of 1.8 nm were uniformly dispersed on the surface of RGO sheets. The as-prepared PtNP–RGO composites as supercapacitor electrodes displayed a specific capacitance of 154 F g−1 at a current density of 0.1 A g−1 and the value retained as high as 72.3% at 20 A g−1 which was significantly enhanced compared to 16.2% capacity retention of RGO prepared by the same method. The investigation of electrochemical performances suggests that PtNPs play an important role in enhancing supercapacitor performance with high rate capability by accelerating the electron transfer and increasing the electrochemical active surface area of RGO.