Wenkun Zhu

One-step hydrothermal synthesis of iron and nitrogen co-doped TiO2 nanotubes with enhanced visible-light photocatalytic activity

TiO2 nanotubes co-doped with iron and nitrogen were successfully synthesized with commercial TiO2 powders (CTPs) using a one-step hydrothermal method. The morphology, structure and composition of the as-prepared nanotubes were characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis), photoluminescence (PL) spectroscopy and Raman spectroscopy. The photocatalytic activities of the samples are evaluated for the degradation of tannic acid (TA, 25 mg L−1) in aqueous solutions under visible light (λ > 420 nm). The results of TEM suggest that all the samples present a diameter of approximately 9 nm and a length of approximately 200–600 nm. The results of XRD suggest that the predominant phase of all the as-prepared samples was the anatase crystal. The XPS results indicate that Fe and N were successfully introduced into the TiO2 nanotubes (TNTs). Compared with the CTPs and pure TNTs, the Fe and N co-doped TiO2 nanotubes (Fe/N-TNTs) exhibit a stronger visible-light absorption capability, and an enhanced photocatalytic activity toward the photodegradation of TA aqueous solution under visible-light irradiation. Notably, the xFe/N-TNT catalysts can be easily recycled due to their one-dimensional nanostructural properties.

Mesoporous gold sponges: electric charge-assisted seed mediated synthesis and application as surface-enhanced Raman scattering substrates

Mesoporous gold sponges were prepared using 4-dimethylaminopyridine (DMAP)-stabilized Au seeds. This is a general process, which involves a simple template-free method, room temperature reduction of HAuCl4·4H2O with hydroxylamine. The formation process of mesoporous gold sponges could be accounted for the electrostatic interaction (the small Au nanoparticles (~3 nm) and the positively charged DMAP-stabilized Au seeds) and Ostwald ripening process. The mesoporous gold sponges had appeared to undergo electrostatic adsorption initially, sequentially linear aggregation, welding and Ostwald ripening, then, they randomly cross link into self-supporting, three-dimensional networks with time. The mesoporous gold sponges exhibit higher surface area than the literature. In addition, application of the spongelike networks as an active material for surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol (4-ATP) molecules as a probe.

High Performances of Artificial Nacre-Like Graphene Oxide-Carrageenan Bio-Nanocomposite Films

This study was inspired by the unique multi-scale and multi-level ‘brick-and-mortar’ (B&M) structure of nacre layers. We prepared the B&M, environmentally-friendly graphene oxide-carrageenan (GO-Car) nanocomposite films using the following steps. A natural polyhydroxy polymer, carrageenan, was absorbed on the surface of monolayer GO nanosheets through hydrogen-bond interactions. Following this, a GO-Car hybridized film was produced through a natural drying process. We conducted structural characterization in addition to analyzing mechanical properties and cytotoxicity of the films. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses showed that the nanocomposite films had a similar morphology and structure to nacre. Furthermore, the results from Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Thermogravimetric (TG/DTG) were used to explain the GO-Car interaction. Analysis from static mechanical testers showed that GO-Car had enhanced Young’s modulus, maximum tensile strength and breaking elongation compared to pure GO. The GO-Car nanocomposite films, containing 5% wt. of Car, was able to reach a tensile strength of 117 MPa. The biocompatibility was demonstrated using a RAW264.7 cell test, with no significant alteration found in cellular morphology and cytotoxicity. The preparation process for GO-Car films is simple and requires little time, with GO-Car films also having favorable biocompatibility and mechanical properties. These advantages make GO-Car nanocomposite films promising materials in replacing traditional petroleum-based plastics and tissue engineering-oriented support materials.

Preparation and Perfomance of an Aging-Resistant Nanocomposite Film of Binary Natural Polymer–Graphene Oxide

As one of the materials having a bionic structure, nacrelike layered composites, inspired by their natural hybrid structures, have been studied via a variety of approaches. Graphene oxide (GO), which differed from inert graphene, was used as a new building block because it could be readily chemically functionalized. Rather than natural polymers, synthetic polymers were most commonly used to fabricate nacrelike GO–polymer materials. However, naturally occurring polymers complied more easily with the requirements of biocompatibility, biodegradability, and nontoxicity. Here, a simple solution-casting method was used to mimic natural nacre and fabricate a self-assembled and aging-resistant binary natural polymer, (κ-carrageenan (κ-CAR)–Konjac glucomannan (KGM))–GO nanocomposites, with varying GO concentrations. The investigation results revealed that κ-CAR–KGM and GO mostly self-assemble via the formation of intermolecular hydrogen bonds to form a well-defined layered structure. The mechanical properties of the natural polymer–GO films were improved significantly compared to those of pure natural polymer films. With the addition of 7.5 wt % GO, the tensile strength (TS) and Young’s modulus were found to increase by 129.5 and 491.5%, respectively. In addition, the composite films demonstrated high reliability and aging resistance as well as a definite TS after cold and hot shock and ozone aging tests, especially showing a superior ozone resistance. The composite films can potentially be used as biomaterials or packing materials.

Biomineralization of varied calcium carbonate crystals by the synergistic effect of silk fibroin/magnesium ions in a microbial system

The influence of silk fibroin (SF) and magnesium ions (Mg2+) on calcium carbonate (CaCO3) bio-mineralization has been investigated. However, the morphology of CaCO3 controlled by the synergistic effect of SF and magnesium ions has not been reported in microbial mineralization systems. Here, we provide novel experimental insights into the role of SF and Mg2+ in the crystallization of CaCO3 in microbial mineralization systems. The morphology and crystallization of CaCO3 aggregates are affected by the self-assembly of SF molecules and the inhibition of Mg2+. This combination promoted the growth of a novel, rod-like superstructure of calcite crystals by aggregating/assembling behavior and crystallization kinetics. In addition, prism-shaped and hemispherical CaCO3 crystal superstructures were obtained in the presence of Mg2+ and SF, respectively. Furthermore, CaCO3 crystals with well-defined morphologies and polymorphs can be obtained by regulating the crystallization conditions (mineralization time and the amount of the additives). The above system has potential applications in the design and preparation of numerous inorganic materials with novel morphologies and specific textures.

High-Strength Konjac Glucomannan/Silver Nanowires Composite Films with Antibacterial Properties

Robust, high-strength and environmentally friendly antibacterial composite films were prepared by simply blending konjac glucomannan (KGM) and silver nanowires (Ag NWs) in an aqueous system. The samples were then characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetric analysis, mechanical property tests, Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS) and antimicrobial tests. The results showed that there was a high ratio of Ag NWs uniformly distributed in the composite films, which was vital for mechanical reinforcement and stable antibacterial properties. The enhanced thermal stability and mechanical intensity increased, while the elongation at break was reduced with an increase in the amount of Ag NWs found in the composite films. When the percentage of Ag NWs in the composite films reached 5%, the tensile strength was 148.21 MPa, Young’s modulus was 13.79 GPa and the ultimate strain was 25.28%. Antibacterial tests showed that the KGM films had no antibacterial effect. After the addition of Ag NWs, the composite films had an obvious inhibitory effect on bacteria, with the uniform dispersion of Ag NWs promoting the antibacterial effect to a certain degree. These results indicated that these composite films would have a potential application in the fields of environmentally friendly packaging or medicine.

A biomass carbon mass coated with modified TiO2 nanotube/graphene for photocatalysis

Powdered modified TiO2 materials are commonly used for photocatalysis. They are easily dispersed in solution but difficult to recycle. In addition, the low light transmission and lack of oxygen in solution also cause a decrease of the photocatalytic efficiency for practical applications. Here we prepare a low-density circular slice which can be suspended on the surface of an aqueous solution and can be used to enrich methylene blue easily. The body of the circular slice is a kind of biomass carbon derived from fungus while the surface of the circular slice is coated with Fe/N co-doped TiO2 nanotubes and a N-doped graphene composite. The advantages are that the circular slice cannot only be convenient to recycle, but also be easy to receive light and oxygen. According to the photocatalytic activity test, the floatable material consisting of Fe/N-TNTs/NG and fungus shows superb performance on the degradation of methylene blue under simulated solar irradiation, which makes it a promising photocatalytic material.

Synergistic metallogenesis of simulated radionuclide strontium by carbonate-mineralization bacteria/nano-montmorillonite

The urease of carbonate-mineralization bacteria (bacillus) secretion is conducive to the formation of carbonate. At the presence of urea and Sr2+, carbonate-mineralization bacteria could lead to the rapid formation of strontium carbonate precipitation. The mineralization process and efficiency were observed by adding nano-montmorillonite (nano-MMT). The effect of bacillus and bacillus/nano-MMT on the mineralization efficiency of Sr2+ was investigated by atomic spectrophotometer. The results showed that both the bacillus and nano-MMT played an important role in the nucleation, growth, and accumulation of strontium carbonate crystals. And this method can efficiently separate simulated radionuclide strontium from high-level radioactive waste.

Effects of Montmorillonite on the Mineralization and Cementing Properties of Microbiologically Induced Calcium Carbonate

Carbonate mineralization microbe is a microorganism capable of decomposing the substrate in the metabolic process to produce the carbonate, which then forms calcium carbonate with calcium ions. By taking advantage of this process, contaminative uranium tailings can transform to solid cement, where calcium carbonate plays the role of a binder. In this paper, we have studied the morphology of mineralized crystals by controlling the mineralization time and adding different concentrations of montmorillonite (MMT). At the same time, we also studied the effect of carbonate mineralized cementation uranium tailings by controlling the amount of MMT. The results showed that MMT can regulate the crystal morphology of calcium carbonate. What is more, MMT can balance the acidity and ions in the uranium tailings; it also can reduce the toxicity of uranium ions on microorganisms. In addition, MMT filling in the gap between the uranium tailings made the cement body more stable. When the amount of MMT is 6%, the maximum strength of the cement body reached 2.18 MPa, which increased by 47.66% compared with that the sample without MMT. Therefore, it is reasonable and feasible to use the MMT to regulate the biocalcium carbonate cemented uranium tailings.

Fabricating a graphene oxide—bayberry tannin sponge for effective radionuclide removal

Bayberry tannin (BT)–reduced graphene oxide (rGO) sponges have been prepared by self–assembly, with bayberry tannin serving as both reductant and surface functionalization agent. The synthetic method is based on the self-assembly of graphene oxide (GO) sheets into porous hydrogel structures. By varying the weight ratio of GO to BT, a series of sorbents with different densities of organic molecules have been obtained and applied to remove Sr2+ from aqueous solutions. Adsorption isotherms (Langmuir and Freundlich) and kinetics (pseudo-first order and pseudo-second order) have been investigated to discuss the sorption performance of rGO/BT sponges. The rGO/BT (w/w 1:1) sponge shows excellent adsorption properties for Sr2+, with maximum capacities of 67.98 mg g−1. The adsorption capacity is much higher than those in classic Sr2+ adsorbents, such as hydrous manganese dioxide, Egyptian soils, Hydroxyapatite nanoparticles, sodium hexa-titanate nanofibers, Graphene oxide, artificially altered phlogopite(Ca–Phl), and PB/Fe3O4/GO. Adsorption mechanisms have been examined using the x-ray photoelectron spectra of sorbents before and after Sr2+ adsorption, and the results indicate that the sorption of Sr2+ on GO and GO/BT 1.0 is largely depended on oxygen functional groups. The results show that the GO/BT sponge is a promising candidate for adsorbing Sr2+ ion.