Simple Wet Chemistry Research Articles

Charge transfer and intrinsic electronic properties of rGO-WO3 nanostructures for efficient photoelectrochemical and photocatalytic applications

The synthesis of WO3 plate-like and rGO-WO3 nanostructured catalysts by a new and simple wet chemistry followed by thermal decomposition method is reported. The prepared catalysts were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, Raman spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning transmission electron microscopy techniques and Brunauer-Emmett-Teller surface area measurement. The photoelectrochemical properties and photocatalytic degradation of methylene blue by WO3 and rGO-WO3 nanostructured catalysts under simulated solar light, and visible light respectively was investigated. The incorporation of rGO in WO3 decreased the band gap energy from 2.54 to 2.45eV which also hindered the recombination rate of photogenerated electron-hole pairs and improved the electron transport properties. The plate-like structure of WO3 and rGO-WO3 nanostructured catalysts was observed from FESEM and TEM techniques. 5.3 and 4.2 folds higher photon-to-hydrogen conversion efficiency by rGO-WO3 photoanode at 0.08 and 0.30V respectively than WO3 photoanode was demonstrated. The photocatalytic activity of WO3 for the degradation of MB was also improved by forming a composite with rGO. The mechanism of the photoelectrochemical and photocatalytic process was discussed. This study provides a simple and scalable pathway to produce highly efficient rGO-WO3 nanostructured photocatalyst for harvesting solar energy efficiently.

NiCo2O4 surface coating Li[Ni0.03Mn1.97]O4 micro-/nano- spheres as cathode material for high-performance lithium ion battery

Abstract Here we report a novel transitional metal oxide (NiCo 2 O 4 ) coated Li[Ni 0.03 Mn 1.97 ]O 4 micro-/nano- spheres as high-performance Li-ion battery cathode material. A thin layer of ∼10 nm NiCo 2 O 4 was formed by simple wet-chemistry approach adjacent to the surface of Li[Ni 0.03 Mn 1.97 ]O 4 micro-/nano- spheres, leading to significantly enhanced battery electrochemical performance. The optimized sample(1 wt%) not only delivers excellent discharge capacity and cycling stability improvement at both room temperature and elevated temperatures, but also effectively prevents Mn dissolution while retaining its coating structure intact according to XRF and TEM results. The CV and EIS break-down analysis indicated a much faster electrochemical reaction kinetics, more reversible electrode process and greatly reduced charge transfer and Warburg resistance, clearly illustrating the dual role of NiCo 2 O 4 coating to boost electron transport and Li + diffusion, and alleviation of manganese dissolving. This approach may render as an efficient technique to realize high-performance lithium ion battery cathode material.

Reduced graphene oxide encapsulated Cu2O with controlled crystallographic facets for enhanced visible-light photocatalytic degradation

The Cu2O/reduced graphene oxide (Cu2O/rGO) composites with effective crystallographic facet controlling of Cu2O crystals were fabricated through a simple one-step wet chemistry method. The crystallographic facet-dependent photocatalytic performance of Cu2O was confirmed, favoring the cuboctahedral Cu2O with {100} and {111} facets and a better photocatalytic activity when compared to cubic and octahedral ones. This was attributed to the slight difference of surface energy between {100} and {111} facets which served as a driving force to promote the separation of photogenerated electron–hole pairs. Moreover, the introduction of two-dimensional rGO sheets could accelerate the transfer of photogenerated electrons from Cu2O to rGO, which further promoted the separation of photogenerated electron–hole pairs and the degradation of methyl orange (MO) under visible-light irradiation. The cuboctahedral Cu2O/rGO composite exhibited a superb photocatalytic performance with the degradation percentage of MO about 97.6% after one periodic photocatalysis due to the synergistic effect of cuboctahedral Cu2O and rGO sheets, foreboding its potential application as photocatalyst.

Improving the optoelectronic properties of titanium-doped indium tin oxide thin films

The focus of this study is on a sol–gel method combined with spin-coating to prepare high-quality transparent conducting oxide (TCO) films. The structural, morphological, optical and electrical properties of sol–gel-derived pure and Ti-doped indium tin oxide (ITO) thin films were studied as a function of the concentration of the Ti (i.e. 0 at%, 2 at% and 4 at%) and annealing temperatures (150 °C–600 °C). FESEM measurements indicate that all the films are ∼350 nm thick. XRD analysis confirmed the cubic bixbyite structure of the polycrystalline indium oxide phase for all of the thin films. Increasing the Ti ratio, as well as the annealing temperature, improved the crystallinity of the films. Highly crystalline structures were obtained at 500 °C, with average grain sizes of about 50, 65 and 80 nm for Ti doping of 0 at%, 2 at% and 4 at%, respectively. The electrical and optical properties improved as the annealing temperature increased, with an enlarged electronic energy band gap and an optical absorption edge below 280 nm. In particular, the optical transmittance and electrical resistivity of the samples with a 4 at% Ti content improved from 87% and 7.10 × 10−4 Ω.cm to 92% and 1.6 × 10−4 Ω.cm, respectively. The conductivity, especially for the annealing temperature at 150 °C, is acceptable for many applications such as flexible electronics. These results demonstrate that unlike the more expensive and complex vacuum sputtering process, high-quality Ti-doped ITO films can be achieved by fast processing, simple wet-chemistry, and easy doping level control with the possibility of producing films with high scalability.

CuS nanoagents for photodynamic and photothermal therapies: Phenomena and possible mechanisms

Photodynamic therapy (PDT) and photothermal therapy (PTT) have been emerging as attractive and promising methods for tumor treatment in clinical approaches. CuS nanoparticles are effective and cost-effective agents for PTT. Recently, it was observed that CuS nanoparticles are also excellence candidates for PDT. However, the mechanisms for CuS nanoparticles as PDT agents have never been discussed. The goal here is to explore the killing mechanisms of CuS nanoparticles as PTT and PDT agents. CuS nanoparticles were synthesized by a simple wet chemistry method by coating with amphiphilic polymer and examined for their therapeutic potential on lung adenocarcinoma cell line SPC-A-1 in vitro and in vivo using a murine cancer model. The CuS nanoparticles produce heat as well as reactive oxygen species (ROS) when excited by 808nm laser and show strong anticancer effects both in vitro and in vivo. The heating effects and release of copper ions from CuS upon heating in the tumor acidic environments are the main mechanisms for the generation of reactive oxygen species which are lethal bullets for cancer destruction. As a dual-function agent for PTT and PDT, CuS nanoparticles are promising phototherapy agents for cancer treatment.

Facile wet-chemical synthesis and efficient photocatalytic hydrogen production of amorphous MoS3 sensitized by Erythrosin B

Herein, an amorphous MoS3 sample suitable for cost-effective and large-scale photocatalytic hydrogen production was prepared via a very simple and practicable wet chemistry method. Using Erythrosin B (EB) as sensitizer, the obtained MoS3 exhibits much higher hydrogen evolution performance (1190.0μmolh−1) than the most extensively studied crystalline MoS2 (180.9μmolh−1) prepared by widely-used hydrothermal method. In addition, the stabilities of MoS3 and EB-MoS3 system were evaluated. Series of analyses indicated that similar to previous reports, gradual composition change from MoS3 to MoS2 happens during the H2 evolution process and the amorphous MoS2 formed is the actual active species for H2 evolution. However, further extensive studies showed that except for photodegradation of EB, activity decrease during long-term or recycling test should mainly originate from the occupation of partial active sites on catalyst surface by some species existing in the reaction mixture, but not from the transformation from amorphous MoS2 to crystalline one. We think that this amorphous MoS3 is a promising material for photocatalytic hydrogen production.

Graphene/Intermetallic PtPb Nanoplates Composites for Boosting Electrochemical Detection of H2O2 Released from Cells.

Rational design and construction of electrocatalytic nanomaterials is vital for improving the sensitivity and selectivity of nonenzymatic electrochemical sensors. Here, we report a novel graphene supported intermetallic PtPb nanoplates (PtPb/G) nanocomposite as an enhanced electrochemical sensing platform for high-sensitivity detection of H2O2 in neutral solution and also released from the cells. The intermetallic PtPb nanoplates are first synthesized via a simple wet-chemistry process and subsequently assembled on graphene via a solution-phase self-assembly approach. The obtained nanocomposite exhibits excellent electrocatalytic activity for the electrochemical reduction of H2O2 in a half-cell test and can detect H2O2 with a wide linear detection range of 2 nM to 2.5 mM and a very low detection limit of 2 nM. Under the same conditions, the sensitivity of PtPb/G for the detection of H2O2 is more than 12.7 times higher than that of commercial Pt/C. The high-density of electrocatalytic active sites on the unique PtPb nanoplates and the synergistic effect between PtPb nanoplates and graphene appear to be the main factors in contributing to the outstanding electroanalytical performance. The PtPb/G can be also used for the practical detection of H2O2 released from Raw 264.7 cells.

Influence of the ZnO nanoarchitecture on the electrochemical performances of binder-free anodes for Li storage

Zinc oxide nanoarchitectures may be employed as binder-free, high specific capacity anodes for lithium batteries. By means of simple and low-impact wet chemistry approaches, we synthesized 1D (nanorods), 2D (single- and multi-layered nanosheets), and 3D (nanobrushes) ZnO arrays. These nanoarchitectures were compared as far as concerns their electrochemical properties and the structural modifications upon lithiation/delithiation. The best results were offered by 2D nanosheets, which showed reversible capacity of the order of 400mAhg−1 after 100 cycles at 1Ag−1. This was due to: i) small nanoparticles, with average diameter of about 10nm, which maximize the array specific surface area and favor the formation of the LiZn alloy; ii) the presence of a mesoporous texture, which allows larger space for accommodating the volume changes upon lithiation/delithiation. However, also these 2D structures showed large irreversible capacity losses. Our work highlights the need for more efficient buffering solutions in ZnO binder-free nanostructured anodes.

Direct Electrodeposition of Thin Metal Films on Functionalized Dielectric Layer and Hydrogen Gas Sensor

Harnessing cathodic hydrogen atom generation, metals such as Pt, Pd, Cu, Au and Ni are directly electrodeposited on functionalized dielectric layers of 6 nm thick silicon oxide formed by thermal oxidation of c-Si substrate. Modifying the oxide layer with functional molecules and Au nanoparticles by simple wet chemistry, we can enhance electrodeposition efficiently and thereby electroplate nanoparticles of Pd and Pt to obtain such thin metal films. In particular, Au nanoparticles on amine-modified silicon oxides remarkably enhance electrodeposition of metal nanoparticles to create sturdy metal films on the dielectric layer, n+-Si/SiO2-NH2. Such enhancement is ascribed to good affinity of Au nanoparticles with electrodeposited metal as well as enhanced current density across the silicon oxide. For an example of potential applications, we show one-step electrodeposition Pd film on dielectric layers to fabricate conductometric hydrogen gas sensor without transferring Pd film.

Photocatalytic removal of NOxusing TiO2-coated zeolite

Application of photocatalytic nanoparticles has been recently gaining an increased attention as air purifying material for sustainable urban development. The present work reports the photocatalytic removal of gaseous phase nitrogen oxides (NOx) using TiO2-coated zeolite to be applied as a filter media for the urban green infrastructure such as raingardens. The TiO2-coated zeolite was synthesized by simple wet chemistry method and tested in a continuous-flow photo-reactor for its removal efficiency of NOx under different conditions of the weight percentage of TiO2 coated on the zeolite, and gas retention time. The removal efficiency of NOx in general increased as the weight percentage of TiO2 coated on the zeolite increased up to 15-20%. Greater than 90% of NOx was removed at a retention time of one minute using the TiO2-coated zeolite (TiO2 weight percentage = 20%). Overall, TiO2-coated zeolite showed greater efficiency of NOx removal compared to TiO2 powder probably by providing additional reaction sites from the porous structure of zeolite. It was presumed that the degradation of NOx is attributed to both the physical adsorption and photocatalytic oxidation that could simultaneously occur at the catalyst surface.

Impacts of oxygen vacancies on the electrocatalytic activity of AuTiO2 nanocomposites towards oxygen reduction

Nanocomposites based on metal nanoparticles supported on oxide surfaces have been used extensively as effective catalysts for fuel cell electrochemistry. In this study, functional nanocomposites based on gold nanoparticles deposited onto TiO2 colloids were prepared by a simple wet chemistry method, and subject to hydrothermal treatment at a controlled temperature in the presence of ascorbic acid. Transmission electron microscopic measurements showed that the gold nanoparticles (10–30 nm in diameter) were embedded within the TiO2 matrix consisting of colloids of 5–10 nm in diameter and anatase crystalline structures, as evidenced in x-ray diffraction studies. Interestingly, electron paramagnetic resonance measurements showed the formation of oxygen vacancies after hydrothermal treatment and the concentrations of oxygen vacancies increased with the amount of ascorbic acid added. Consistent results were obtained in x-ray photoelectron spectroscopic measurements, which suggested partial charge transfer from gold to oxygen-deficient TiO2. The Au:Ti atomic ratio in the nanocomposites was estimated to be ca. 11% and consistent among the series of samples. Electrochemically, the nanocomposites exhibited apparent electrocatalytic activity towards oxygen reduction reactions in alkaline media, which showed a peak-shaped variation with the concentration of the oxygen vacancies. This was accounted for by the deliberate manipulation of the binding energy of oxygen species onto the nanocomposite surfaces. In addition, the AuTiO2 nanocomposites exhibited markedly enhanced tolerance against methanol crossover, as compared to commercial Pt/C catalysts.

Solution-processable graphenes by covalent functionalization of graphene oxide with polymeric monoamines

We develop here a simple wet chemistry to prepare covalent functionalized graphenes (FGs) through epoxide aminolysis especially under alkaline aqueous condition. Remarkably, a series of typical monoamines, such as industrial Huntsman Jeffamine® M-2070 and M-2005 polymer with hydrophilic or hydrophobic polyetheramine chains, positively-charged 2-amino-N,N,Ntrimethylpropanaminium, negatively-charged sulfanilic acid, even oligopeptide sequence, can be effectively grafted on the platelets of graphene oxide precursor with covalent functionalization and partially reduced features. This strategy provides the researchers a facile and convenient approach to design and synthesize solution processable, biocompatible and functionalized graphenes for the potent applications in electronic inks, drug carriers and biomedicines. Expansion of the current study is actively ongoing in our laboratory.

The electrochemical behaviors of Li2C8H4O6 and its corresponding organic acid C8H6O6 as anodes for Li-ion batteries

Abstract A functional organic small molecule anode material (dilithium 2,5-dihydroxyterephthalate, Li 2 DHTP) is synthesized via a simple wet chemistry methodology adopting 2,5-dihydroxyterephthalic acid (DHTPA) as the precursor. It delivers a high specific capacity of 165 mAh/g over 100 cycles with the coulombic efficiency of 98% and shows remarkable rate performance. The organic acid DHTPA also demonstrates electrochemical activity toward Li + storage and releases but with poor cyclic performance. XRD and FT-IR studies suggest that the de −/lithiation process of chemically replaced Li 2 DHTP is highly reversible. On the contrary, the de −/lithiation process of electrochemically replaced Li 2 DHTP intermediate product, where the corresponding DHTPA acid experiences an ion exchange process in the first discharge process, shows quite poor reversibility in the following cycles. The results illustrate that either chemical replacement or electrochemical replacement of DHTPA can generate Li 2 DHTP electrochemical active material. This methodology might be applied to synthesize advanced organic small molecules conjugated carbonyl materials for energy storage.

Photoelectrocatalytic hydrogen production by water splitting using BiVO4 photoanodes

Nanocrystalline bismuth vanadate was deposited by simple wet chemistry procedure on FTO electrodes in order to construct visible light responsive photoanodes, which were employed for photoelectrochemical hydrogen production by water splitting. The specific surface area of the films was controlled by the presence of a surfactant template (Triton X-100). It was, however, found that when the quantity of surfactant was relatively high, the stoichiometry of the photocatalyst as well as its activity was lost. The obtained materials were characterized by SEM, XRD, AFM, BET and UV–Vis spectroscopy. Optimized photoanodes were employed in photoelectrochemical cells for water splitting and hydrogen production under electric and chemical bias. Maximum hydrogen production rate was 0.15mmol/h under electric bias of 1.4V vs Ag/AgCl plus 0.37V chemical bias.

A general method for the synthesis of graphene oxide-metal sulfide composites with improved photocatalytic activities

A simple wet chemistry method was employed for the synthesis of graphene oxide-metal sulfide composites. The obtained products were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen absorption–desorption specific surface area and UV–Vis spectroscopy. The study indicates that sulfides nanorods were well dispersed on the graphene oxide nanosheets in the graphene oxide-metal sulfide composites. It was found that the specific surface area of the composites increased with the introduction of graphene oxide. The as-synthesized graphene oxide-metal sulfide composites were used as photocatalysts for the color removal of methyl orange under UV light irradiation. The results indicated that the graphene oxide-metal sulfide composites exhibited improved photocatalytic activity to pure sulfides and commericial sulfides, with nearly 95% and 90% of methyl orange degraded after irradiation for 15 min, respectively. The excellent photocatalytic activity of the composites can be ascribed to the high specific surface area and the reduction of photoinduced electron–hole pair recombination due to the introduction of graphene oxide. With the help of various radical scavengers, O2− and h+ were proved to be the main reactive species for the color removal of methyl orange.

Post-Synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals.

Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein, we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, by an acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, along these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution.

Performance Enhancement of Activated Carbon Based Supercapacitors By Incorporation of Fullerene Self-Assemblies

The deployment of renewable energy based power-grids, the development of next-generation high-efficiency hybrid/fully electric-vehicles with extended per-charge mileage, and the design and fabrication of cutting-edge energy-efficient portable electronic devices, all require robust, long cycle-lifetime energy storage systems with exceptional energy-density and power-density properties. In this context, supercapacitors could play a potential role in satisfying the above needs. Currently, activated carbon (AC) is the electrode material of choice, though there is a big push towards developing newer carbon nanostructure based electrodes due to some pitfalls associated with AC. Specifically, AC suffers from low electrical conductivity, and additionally demonstrates a broad range of porosities, which is shown to adversely affect the device performance. As a consequence, conductive additives are used for reducing resistance, but they adversely affect the available specific surface area of the electrode. Further, AC has also been combined with other carbon nanostructures such as graphene and carbon nanotubes (CNT) in an effort to increase electrode conductivity. In addition, it was seen that the nanostructures also increase available surface area, leading to an increase in power density, as well as specific capacitance. However, the increase in capacitive performance of AC systems due to graphene and CNT requires significant amount (30-50 %) of an addition of these structures, which has a huge impact on the overall cost of fabrication. Further, in contrast to the numerous investigations on AC-graphene and AC-CNT composite based electrodes, not much work has focused on the addition of fullerene to AC. In this work, the ability to further increase the energy and power density performance of AC based supercapacitors by the incorporation of carbon nanostructures is demonstrated. Specifically, using an easy-to-fabricate method that enables rapid self-assembly of fullerene (C60) nanotubes and nanorods, light weight supercapacitor electrodes that also incorporate commercially available AC were developed. The presence of graphene over the current collector and fullerene self-assembly over the graphene grown copper current collectors were also studied. Of note is the fact that the developed method relies on simple wet-chemistry based procedures, and is therefore completely scalable as well as compatible with existing device fabrication methods. A specific capacitance enhancement of 50 % was observed due to the addition of the fullerene self-assemblies along with graphene grown current collectors as compared to fullerene-free systems on just bare current collectors. These electrode systems were also accompanied by a simultaneous increase in max power density by 20%, 94% capacitance retention even after 5000 cycles interestingly, the mass fraction of the fullerenes as compared to activated carbon is less than 1%. The substantial increase in performance is attributed to the meso and micro-porosity of the fullerene self-assemblies. While we have focused on enhancing the performance of low-cost AC based systems in this work, the inclusion of the fullerene self-assemblies within any carbon based electrode should lead to similar performance enhancements.

Modulating Electrical Properties of InAs Nanowires via Molecular Monolayers.

In recent years, InAs nanowires have been demonstrated with the excellent electron mobility as well as highly efficient near-infrared and visible photoresponse at room temperature. However, due to the presence of a large amount of surface states that originate from the unstable native oxide, the fabricated nanowire transistors are always operated in the depletion mode with degraded electron mobility, which is not energy-efficient. In this work, instead of the conventional inorganic sulfur or alkanethiol surface passivation, we employ aromatic thiolate (ArS(-))-based molecular monolayers with controllable molecular design and electron density for the surface modification of InAs nanowires (i.e., device channels) by simple wet chemistry. More importantly, besides reliably improving the device performances by enhancing the electron mobility and the current on-off ratio through surface state passivation, the device threshold voltage (VTh) can also be modulated by varying the para-substituent of the monolayers such that the molecule bearing electron-withdrawing groups would significantly shift the VTh towards the positive region for the enhancement mode device operation, in which the effect has been quantified by density functional theory calculations. These findings reveal explicitly the efficient modulation of the InAs nanowires' electronic transport properties via ArS(-)-based molecular monolayers, which further elucidates the technological potency of this ArS(-) surface treatment for future nanoelectronic device fabrication and circuit integration.

Peanut shaped ZnO microstructures: controlled synthesis and nucleation growth toward low-cost dye sensitized solar cells

This paper describes a simple, low-temperature and cost effective chemical precipitation method in aqueous media to synthesis uniformly distributed zinc oxide (ZnO) microstructures for the fabrication of dye-sensitized solar cells (DSSCs). The size and morphology of the ZnO microstructures are systematically controlled by adjusting the concentration of the precursors, zinc acetate dihydrate and ammonium hydroxide. X-ray diffraction (XRD) and scanning electron microscopy are used for the structural characterizations and photoluminescence and Fourier transform infrared spectroscopy are used to characterize the optical properties of the ZnO, respectively. The results reveal that ZnO crystallites exhibit hexagonal wurtzite structure with preferential orientation along c-axis. The effect of ammonia concentration on the crystallinity, morphology and optical properties of ZnO microstructures and the concomitant effect on the efficiency of DSSCs is also quantified. The peanut-shaped ZnO microstructure, which was found to increase DSSCs performance over other microstructure, is studied in detail in order to develop a formation mechanism. A sandwich type eosin yellow sensitized solar cell is prepared using peanut-shaped ZnO microstructures, which showed an efficiency of 0.37%. Ammonia was found to play a crucial role in the evolution of ZnO morphologies. These results are promising and provide a path towards low-cost high-performance DSSCs based on peanut-shaped ZnO microstructures and produced with only relatively simple wet chemistry synthesis.

Bio-inspired functionalization and redox charge transfer of graphene oxide sponges for pseudocapacitive electrodes

Bio-inspired and environmentally friendly chemical functionalization method for reducing of graphene oxide (GO) sponge using dopamine derivatives is developed. The GO sponge is readily modified by poly(norepinephrine) (p(Nor)) through a simple wet chemistry, and mechanical properties of the GO sponge is improved with structural stability. The oxidative polymerization of norepinephrine can considerably remove oxygen-containing species from the GO sponge surface as well as provide redox active quinone moieties for pseudocapacitive electrodes. Furthermore, three-dimensional (3D) macroporous networks of the reduced GO (rGO) sponge provide a large surface area and continuous ion pathways. As a result, p(Nor)-functionalized rGO (p(Nor)@rGO) sponge exhibits enhanced capacitive performance. The p(Nor)@rGO sponge shows that a specific capacitance of 232.1Fg−1 (2.5 times higher than that of chemically converted rGO sponge) and good cyclic stability over 2000 charge/discharge cycling tests.