An electrically conductive, flow-through, fixed bed adsorption membrane (FCME) made of carbon nanotubes (CNT) installed in an electrochemical flow cell, was applied for the highly efficient adsorption and detection of organic pollutants. Three analytes with different chemical nature, i.e., parathion ethyl, tartrazine and diquat, were chosen as model systems to demonstrate the capabilities of the system. Adsorptive stripping voltammetry (AdSV) performed by the FCME provided directly the amount of analyte adsorbed; in contrast to an adsorption column, that monitors the effluent concentration. The adsorption capacity and kinetic constants were obtained by AdSV and were comparable with those predicted by the Thomas model. The FCME enabled the detection of nanomolar levels of tartrazine and parathion, and submicromolar levels of diquat with a linear range of three orders of magnitude. In addition to being a very sensitive analytical tool, FCME is an adsorption membrane that enables its simple electrochemical regeneration.
We studied the direct electron transfer (DET) between glucose and electrogenerated AuCl4- catalysed by glucose oxidase (GOx) and gold nanoparticles (AuNPs) by scanning electrochemical microscopy (SECM). Well-defined AuNPs were prepared and attached onto an insulating surface. Studying the current transients of a gold microelectrode held within a few microns from the surface revealed that the AuNPs interacted with the GOx and were crucial for the DET from the glucose. We investigated very carefully the effect of pH and the size of the AuNPs on electron transfer. AuNPs of 16, 40 and 80 nm diameter were applied. The kinetics of electron transfer was analysed by the Michael-Menten kinetic mechanism. Interestingly, we found that the fastest DET was exhibited by the 40 nm AuNPs at pH 3 and 5. At higher pH, electron transfer was better catalysed by the 80 nm AuNPs. This was rationalized by the effect of the pH on the enzymatic structure and the charge of the AuNPs.
The selective recognition of nanoparticles (NPs) can be achieved by nanoparticle-imprinted matrices (NAIMs), where NPs are imprinted in a matrix followed by their removal to form voids that can reuptake the original NPs. The recognition depends on supramolecular interactions between the matrix and the shell of the NPs, as well as on the geometrical suitability of the imprinted voids to accommodate the NPs. Here, gold NPs stabilized with citrate (AuNPs-cit) were preadsorbed onto a conductive surface followed by electrografting of p-aryldiazonium salts (ADS) with different functional groups. The thickness of the matrix was carefully controlled by altering the scan number. The AuNPs-cit were removed by electrochemical dissolution. The recognition of the NAIMs was determined by the reuptake of the original AuNPs-cit by the imprinted voids. We found that the recognition efficiency is a function of the thickness of the NAIM layer and is sensitive to the chemical structure of the matrix. Specifically, a subtle change of the functional group of the p-aryldiazonium building block, which was varied from an ether to an ester, significantly affected the recognition of the NPs.
Renewable energy technology and effective energy management are the most crucial factors to consider in the progress toward worldwide energy sustainability. Smart window technology has a huge potential in energy management as it assists in reducing energy consumption of indoor lighting and air-conditioning in buildings. Electrochromic (EC) materials, which can electrically modulate the transmittance of solar radiation, are one of the most studied smart window materials. In this work, highly transparent SnO2 inverse opal (IO) is used as the framework to electrochemically deposit amorphous WO3 layer to fabricate hybrid SnO2-WO3 core-shell IO structure. The hybrid structure is capable of effective near infrared (NIR) modulation while maintaining high visible light transparency in the colored and bleached states. By varying the initial diameter of the polystyrene (PS) opal template and the WO3 electrodeposition time, optimal results can be obtained with the smallest PS diameter of 392 nm and 180 s WO3 electrodeposition. In its colored state, the 392-SnO2-WO3-180 core-shell IO structure shows approximate to 70% visible light transparency, 62% NIR blockage at 1200 nm, and approximate to 15% drop in NIR blocking stability after 300 cycles. The SnO2-WO3 core-shell IO structure in this study is a promising EC material for advanced smart window technology.
Binder-free electrodes with core-shell structures have shown great potential in a variety of important energy storage systems. In order to endow the core-shell hierarchical structure with enhanced electrochemical properties, rationally designed and fabricated hierarchical structures with controllable morphology and great electrical conductivity are highly desired. In this work, a uniform dendritic SCo3O4@NiCo2S4 hierarchical structure grown on Ni foam was successfully designed and synthesized via sulfur-doping of Co3O4 (S-Co3O4) as the inner core with enhanced conductivity. The hierarchical electrode exhibited high areal capacity (10.9 mA h cm(-2) at a current density of 8 mA cm(-2)), a good rate performance (72.5% retention after increasing the current densities from 8 to 30 mA cm(-2)), and excellent cycling stability (97.3% retention after 5000 cycles). Moreover, a hybrid energy storage batterysupercapacitor device, constructed from a S-Co3O4@NiCo2S4 positive electrode and an active carbon (AC) negative electrode, showed high energy density and power density. Contributing to short ion diffusion, large electroactive sites and low contact resistance, our work not only demonstrates a promising electrode for energy storage battery-supercapacitor hybrid (BSH) devices, but also provides an attractive strategy for the design of electrode materials.
Long-term cycling stability is an important criterion and big challenge for pseudocapacitive materials. Ultra-stable manganese doped Co3O4 mesoporous nanoneedles were synthesized via one-step hydrothermal reaction followed by annealing grown on nickel foam (noted as MnxCoyO/NF, x + y = 2.25) for supercapacitors. The Mn doping in Co3O4 was confirmed by several techniques. Among various MnxCoyO/NF electrodes, the Mn1.5Co0.75O/NF demonstrated the superior electrochemical performance, with an excellent cycling stability of 104% capacitance retention after 10 000 charge-discharge cycles at 6 A g(-1), as well as a good capability (668.4 F g(-1) at 1 A g(-1 )compared to that of undoped Co3O4 which is 201.3 F g(-1)). Moreover, the assembled asymmetric supercapacitor based on Mn1.5Co0.75O/NF//graphene performs a high energy density of 25.88 Wh kg(-1) (at 359.5 W kg(-1)) and a high power density of 14.7 kW kg(-1) (at 10.63 Wh kg(-1)). The improved electrochemical properties are mainly owing to the enhanced intrinsic conductivity and electrochemical activity of Co3O4 after doped with appropriate Mn concentration. The three-dimensional nanostructure of mesoporous nanoneedle array grown on NF also provides short ion diffusion path and large active surface areas, contributing to the high rate performance and high energy density. This study may offer a new approach to fabricate the unique 3D nanostructured electrode materials based on doped metal oxides for supercapacitors with long-term cycling stability and high energy density.