Junkui Ma

Cost-Effective Reduced Graphene Oxide-Coated Polyurethane Sponge As a Highly Efficient and Reusable Oil-Absorbent

Reduced graphene oxide coated polyurethane (rGPU) sponges were fabricated by a facile method. The structure and properties of these rGPU sponges were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy. The rGPU sponges are hydrophobic and oleophilic and show extremely high absorption for organic liquids. For all the organic liquids tested, the absorption capacities were higher than 80 g g(-1) and 160 g g(-1) (the highest value) was achieved for chloroform. In addition, the absorption capacity of the rGPU sponge did not deteriorate after it was reused 50 times, so the rGPU sponge has excellent recyclability.

An environmentally friendly method for the fabrication of reduced graphene oxide foam with a super oil absorption capacity

Three kinds of graphene oxide (GO) foams were fabricated using different freezing methods (unidirectional freezing drying (UDF), non-directional freezing drying, and air freezing drying), and the corresponding reduced graphene oxide (RGO) foams were prepared by their thermal reduction of those GO foams. These RGO foams were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The absorption process and the factors that influence the absorption capacity were investigated. The RGO foams are hydrophobic and showed extremely high absorbing abilities for organic liquids. The absorption capacity of the RGO foams made by UDF was higher than 100 g g(-1) for all the oils tested (gasoline, diesel oil, pump oil, lubricating oil and olive oil) and had the highest value of about 122 g g(-1) for olive oil. The oil absorption capacity of the GO foams was lower than that of the RGO foams, but for olive oil, the absorption capacity was still high than 70 g g(-1), which is higher than that of most oil absorbents.

Porous graphene oxide/carboxymethyl cellulose monoliths, with high metal ion adsorption.

Orderly porous graphene oxide/carboxymethyl cellulose (GO/CMC) monoliths were prepared by a unidirectional freeze-drying method. The porous monoliths were characterized by Fourier transform infrared spectra, X-ray diffraction and scanning electron microscopy. Their properties including compressive strength and moisture adsorption were measured. The incorporation of GO changed the porous structure of the GO/CMC monoliths and significantly increased their compressive strength. The porous GO/CMC monoliths exhibited a strong ability to adsorb metal ions, and the Ni(2+) ions adsorbed on GO/CMC monolith were reduced by NaBH4 to obtain Ni GO/CMC monolith which could be used as catalyst in the reduction of 4-nitrophenol to 4-aminophenol. Since CMC is biodegradable and non-toxic, the porous GO/CMC monoliths are potential environmental adsorbents.

Reduction of graphene oxide with L-lysine to prepare reduced graphene oxide stabilized with polysaccharide polyelectrolyte

An environmentally friendly approach to reduce graphene oxide (GO) with L-lysine (L-Lys) was developed by using carboxymethyl starch (CMS) as a stabilizing agent and a stable suspension of reduced graphene oxide (RGO) was obtained. UV visible absorption spectroscopy was used to monitor the deoxygenating process and the factors that affect the GO reduction, such as the ratio of GO/L-Lys, the temperature and pH were optimized. The reduction of the GO was verified by Fourier transform infrared spectroscopy, X-ray diffraction, thermo-gravimetric analysis, Raman spectroscopy and X-ray photoelectron spectroscopy. Ordered porous RGO/CMS foams were prepared by a unidirectional freeze-drying method (UFDM) and used as absorbents for copper ions. Since L-Lys and CMS are natural and edible chemicals, this approach provides a green method to produce stable RGO from GO on a large scale. The nontoxic biodegradable RGO/CMS foams show potential applications for metal ions removal from wastewater.

Response of inverse-opal hydrogels to alcohols

A polyacrylamide inverse-opal hydrogel (IOHPAM) film was synthesized by in situ polymerization in a polystyrene colloidal crystal template. The IOHPAM has a periodically ordered interconnecting porosity that endows the film with a band gap and structural color. The IOHPAM film exhibits a rapid reversible change in volume and in refractive index in response to alcohols and, consequently, the structural color and reflection peak of the IOHPAM film are quickly synchronized with these changes. The reflection peak of the IOHPAM film shows obvious blue or red-shifts that depend on the structure of the alcohols. The extent of the shift not only depends on the number of –OH groups, but also on the chain length, structure and concentration of the alcohols. The IOHPAM film is also sensitive to polyethylene glycol (PEG) and displays different blue-shift responses to PEGs with different molecular weights. Since the IOHPAM films have different reflectance spectra and structural colors in response to different types and concentrations of alcohols, this provides a potential way to visually detect alcohols.

Graphene oxide supported Au?Ag alloy nanoparticles with different shapes and their high catalytic activities

A simple method was developed to fabricate Au-Ag nanoparticle/graphene oxide nanocomposites (Au-Ag/GO) by using simultaneous redox reactions between AgNO3, HAuCl4 and GO. The Au-Ag/GO was characterized by x-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive x-ray spectroscopy. The GO nanosheets acted as the reducing agent and the support for the Au-Ag alloy nanoparticles. In addition, Au-Ag alloy nanoparticles with different shapes including core-shell-like, dendrimer-like and flower-like were obtained by simply modifying the concentration of the reactants and the reaction temperature. With no reducing or stabilizing agents added, the Au-Ag/GO nanocomposites show superior catalytic performance for the reduction of 4-nitrophenol and for the aerobic homocoupling of phenylboronic acid.

Inverse opal hydrogels with adjustable band gaps tuned by polyethylene glycol

Inverse opal hydrogels of polyacrylamide (PAM) with adjustable band gaps (P-IOHspam) were fabricated by changing the molecular weight of polyethylene glycol (PEG), and the amount of PEG and N,N′-methylenebisarcylamide (BIS) in the monomer precursors. After the PEG was removed, mesopores were left in the PAM hydrogels and these caused changes in the band gap of the P-IOHspam. Compared with inverse opal hydrogels of PAM (IOHspam) that were prepared without PEG, the reflection peaks shifted to a longer wavelength which provides a wider usable visible wavelength range. P-IOHspam show rapid shifts in the reflection peak in response to chemicals, such as PEG, glycol, glucose and L-lysine. The shift of the reflection peak is greater for the P-IOHspam made from monomer precursors containing more PEG and for higher molecular weights of PEG. The shifts are caused by changes in two factors: the average refractive index of the P-IOHpam material and the degree of equilibrium swelling of the PAM hydrogel, both of which are sensitive to chemicals. Such sensitive materials could be used as chemical sensors.

Molecularly imprinted photonic crystals for the direct label-free distinguishing of L-proline and D-proline

Novel molecularly imprinted photonic crystals (IPCs) for the highly sensitive label-free detection of L-proline and for the chiral recognition of L/D-proline were reported. A series of L-proline imprinted polyacrylamide photonic crystals (PAM-LPIPCs) and poly(acrylamide-co-acrylic acid) photonic crystals (PAM-co-AA-LPIPCs) were fabricated via the in situ polymerization of polystyrene opal. The PAM-LPIPCs exhibit good molecular response in L-proline solutions and can be visualized by the naked eye much like a pH test paper. The concentration of imprinted molecules (L-proline) in aqueous solution can be detected by the chromatic signal (structural color) or the optical signal (λmax). Furthermore, the responsivity and sensitivity of the PAM-co-AA-LPIPCs can be improved by increasing the amount of the imprinted content or the proportion of AA, or by decreasing the ratio of the cross-linking agent. When all these factors were balanced, a PAM2-co-AA0.4-LP0.5 IPC with good strength, high responsivity, high sensitivity and specific molecular recognition was obtained. It is found that the presented crystals can show obvious response to L-proline solution even at a low concentration of 1%. The PAM2-co-AA0.4-LP0.5 IPC not only very selectively distinguishes between L-proline and nicotinic acid, but it is also good at chiral recognition between L-proline and D-proline. What is more, the response is rapid and reversible and the IPC is recyclable.