Catalyst-free Solution Research Articles

Facile synthesis of porous graphene-like carbon nitride nanosheets with high surface area and enhanced photocatalytic activity via one-step catalyst-free solution self-polymerization

Porous graphite carbon nitride nanosheets (g-C3N4) are achieved via one-step catalyst-free solution self-polymerization from a single melamine precursor. The resultant porous g-C3N4 nanosheets with the best photodegradation capacity provided the surface area of 669.15m2/g, which is superior to the surface area of any other porous g-C3N4 reported. Results showed enhanced adsorption and degradation capacity of methyl orange (MO) under UV-visible light irradiation (λ>350nm) compared to bulk g-C3N4. The MO oxidation of the porous g-C3N4 nanosheets is driven mostly by the participation of holes, and secondly by O2− and OH radicals. This approach shed lights on porous g-C3N4 production simply by self-polycondensation of single functional monomer. It also provided a low-cost and eco-friendly method to facilely mass-produce g-C3N4 nanosheets with high surface area for many potential applications.

Microfluidics Fabrication of Self-Oscillating Microgel Clusters with Tailored Temperature-Responsive Properties Using Polymersomes as "Microreactors".

Poly(N-isopropylacrylamide)-based microgel clusters were successfully prepared using polymersomes as "microreactors", which were fabricated through microfluidics. The clusters were formed from the cross-linking reaction between ruthenium/amino group dual functionalized poly(N-isopropylacrylamide) microgels and linear poly(N-isopropylacrylamide)-r-(N-acryloxysuccinimide)-based polymer linkers under neutral pH conditions. By simply adjusting the ratio of N-isopropylacrylamide to N-acryloxysuccinimide in the polymer cross-linkers, the internal structures of the clusters can be controlled; hence, the temperature response of the clusters can be regulated. It was demonstrated that these different microgel clusters showed various degrees of chemomechanical oscillations when the clusters were exposed to a catalyst-free solution containing Belousov-Zhabotinsky reaction substrates.

Solvothermal synthesis and conductive properties of nanorod-constructed Al-doped ZnO microflowers

Nanorod-constructed Al-doped ZnO (AZO) microflowers were for the first time synthesized by a facile solvothermal route. The synthesis involves a low-cost, template-free, non-seed and catalyst-free solution process to relatively high conductive AZO crystalline. In this process, the morphology of the AZO nanopowders could be effectively controlled by adding the mineralizer or not. With the increase of Al3+ doping content, the electrical resistivity of AZO microflowers decreased firstly and then increased, and which reaches a minimum value of ~647 Ω cm at 2 % Al3+ doping. The formation mechanism of the nanorod-constructed AZO microflowers was also discussed.

Solution phase van der Waals epitaxy of ZnO wire arrays

As an incommensurate epitaxy, van der Waals epitaxy allows defect-free crystals to grow on substrates even with a large lattice mismatch. Furthermore, van der Waals epitaxy is proposed as a universal platform where heteroepitaxy can be achieved irrespective of the nature of the overlayer material and the method of crystallization. Here we demonstrate van der Waals epitaxy in solution phase synthesis for seedless and catalyst-free growth of ZnO wire arrays on phlogopite mica at low temperature. A unique incommensurate interface is observed even with the incomplete initial wetting of ZnO onto the substrate. Interestingly, the imperfect contacting layer does not affect the crystalline and optical properties of other parts of the wires. In addition, we present patterned growth of a well-ordered array with hexagonal facets and in-plane alignment. We expect our seedless and catalyst-free solution phase van der Waals epitaxy synthesis to be widely applicable in other materials and structures.

Low-macroscopic field emission from fibrous ZnO thin film prepared by catalyst-free solution route

Fiber-structured zinc oxide thin films were synthesized by catalyst-free chemical process from zinc acetate dihydrate at an elevated temperature of 1073K on Si substrate. X-ray diffraction spectra confirmed the proper phase formation of the films. Scanning electron micrograph depicted the formation of ZnO fibers with an average diameter of 500nm with an average aspect ratio ∼150. Field emission properties of the film showed considerably low turn-on field around 1.4V/μm. This low-threshold field-emission of the films are attributed to the conducting nanostructure inside the film as well as on the tip of the fibers at the film–vacuum interface, which causes the geometrical field enhancement at the emitter-tip and provides the required barrier field for field-emission tunneling. The emission current was as high as ∼70μA at the field of 3.6V/μm. The high emission current, high stability and low turn-on field make the ZnO fibers a strong candidate for field-emission displays.

A study on dye photoremoval in TiO 2 suspension solution

TiO 2 samples with different characteristics and adsorption ability were prepared via hydrolysis of titanium tetraisopoxide and calcination at four different temperatures. The photoremoval of Acid Red 3B catalyzed by these catalysts was carried out. The results show high firing temperature lead to large TiO 2 particle and a low adsorption ability of TiO 2. The dye photoremoval reaction fits zero order kinetics well in catalyst-free solution and changes to first order kinetics in the presence of TiO 2. The solution pH value has a large effect on the removal efficiency. High dye removal efficiency can be obtained at high pH value. Catalyst addition improves the dye photoremoval efficiency and leads to the change of removal kinetics. Anatase TiO 2 fired at 400 °C shows the best catalytic activity and the catalytic activity of TiO 2 fired at 800 °C, which is rutile, is the worst of all catalysts. The catalytic ability of TiO 2 is influenced mainly by two factors of catalysts: crystalline form and adsorption ability for Acid Red 3B. The crystalline form is a more important factor influencing the catalytic activity than the adsorption ability of TiO 2 and the catalytic activity can be enhanced by the high dye adsorption ability of TiO 2.

Disordered waves in an excitable medium consisting of two layers: Catalytic gel and noncatalytic solution

Disordered waves in the light-sensitive Belousov-Zhabotinsky reaction (``ripples,'' i.e., aperiodic wave front deformations, labyrinthine patterns, and ``frazzle gases,'' i.e., erratically moving wave fragments) were observed experimentally a few years ago, but have so far not been explained and modeled. The system, consisting of a gel with immobilized catalyst covered by a catalyst-free solution, is motionless and horizontally homogeneous. The observed disorder is related to enhancement or breakups of fluctuation valleys. In the model presented here, this destabilization is caused by inhibitor produced in the refractory tail that diffusively surpasses the wave front via the upper solution layer. This is in agreement with experiments both qualitatively, i.e., in the overall appearance of the patterns, as well as quantitatively, regarding the eikonal relationship and autocorrelation analysis.

Photolytic degradation of aqueous hydrogen sulphide with simultaneous hydrogen production using visible light

Hydrogen was photochemically produced from an aqueous, catalyst-free solution containing Ru(bipy), methyl viologen, and hydrogen sulphide as electron donor. This system was most efficient at pH 5 after 4 h irridiation, but the extrapolated turnover number was higher at a somewhat higher pH because of the sensitizer bleached substantially as a function of pH, most serious at low pH. The behaviour of the methyl viologen radical is different to that in similar systems but with EDTA instead of H 2S as electron donor. In systems with EDTA, the methyl viologen radical forms a CT-complex with a proton with p K a = 4.0 whereas with hydrogen sulphide, competing reactions reduce the formation of methyl viologen radicals at pH > 4. Nevertheless, with H 2S three orders of magnitude more hydrogen was produced than with EDTA in catalyst-free solutions.