Surfactant Polyvinylpyrrolidone Research Articles

A novel dual S-scheme heterojunction photocatalyst KBCN/t-BiVO4/m-BiVO4 induced by phase-transformed bismuth vanadate for highly efficient degradation of ciprofloxacin in full-spectrum: Degradation pathway, DFT calculation and mechanism insight

A novel KBr-g-C3N4/t-BiVO4/m-BiVO4 (15KBCN/mtBVO-P, P means PVP) heterojunction photocatalyst is synthesized using a hydrothermal method with the assistance of surfactant polyvinylpyrrolidone (PVP). Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and X-ray powder diffraction (XRD) confirm the formation of the heterostructure and changes in the crystal structure. Under sunlight illumination, 15KBCN/mtBVO-P exhibits the strongest photocatalytic degradation performance for ciprofloxacin (CIP), reaching 95.3 % within 240 min, the apparent kinetic constant is approximately 3.4, 2.4, and 3.3 times higher than CN, t-BVO, and m-BVO. The outstanding CIP degradation rate is observed under simulated solar and visible light, with over 93.0 % and 85.8 % in 60 min and 120 min. The enhanced photocatalytic performance is attributed to the in-situ generation of the mixed-phase BiVO4 by precise crystal phase regulation. Furthermore, the charge transport and photocatalytic degradation mechanism of 15KBCN/mtBVO-P is revealed. Degradation pathways and ecotoxicity of CIP and its degradation products were elucidated through LC-MS/MS technology, DFT calculations, and QSAR models. This study presents a pioneering perspective on the fabrication and development of g-C3N4-based dual S-scheme heterojunction photocatalysts for practical application.

Surfactant-assisted synthesis of plate-like CuS particles for high-performance symmetric capacitor

In this research, plate-like CuS particles were synthesized through a hydrothermal method using cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) as surfactants. The effects of surfactant type and content on the structural, microstructural, and electrochemical properties were explored by the various characterization techniques. Single-phase CuS powders with a space group of P63/mmc were crystallized by decomposition of the copper-thioacetamide complex during hydrothermal treatment. The spherical morphology transformed into plate-like particles by adding the CTAB surfactant, while the PVP surfactant led to an agglomeration of small spherical nanoparticles. With adding the CTAB surfactant, the specific capacitance increased from 630 to 1806 Fg−1 at a current density of 1 Ag−1, while it increased up to 1575 Fg−1 for the PVP surfactant. A symmetric capacitor was assembled on the base of spherical CuS nanoparticles as the negative electrode and the platelike CuS particles as the positive electrode. The CuS//CuS capacitor exhibited comparable electrochemical performance including an energy density of 25.62 Whkg−1 and a power density of 1488 Wkg−1, respectively.

Experimental investigation of thermal energy storage in shell-and-multi-tube unit with nano-enhanced phase change material

This paper deals with thermal energy storage with use of nanoparticle enhanced phase change material in shell-and-multitube unit. The experiments are conducted under atmospheric pressure. Paraffin wax and two different fatty acids are used as base phase change material. Graphite and multi-walled carbon nanotubes serve as nanoparticles. Graphite nanoparticles are tested at the concentrations of 0.1 %, 1 % and 5 % by weight, while multi-walled carbon nanotubes only at 0.1 %wt. Ultrasonic vibration and homogenizer are used in order to stabilize the dispersion of the nanoparticles. Polyvinylpyrrolidone surfactant is used to stabilize the suspension and the tested nano-enhanced phase change material exhibit satisfactory stability. Experimental measurements are performed for a bundle of 7 tubes with outside diameter of 6 mm in a staggered arrangement and a pitch ratio of 4.5. It is found that, regardless of the tested base phase change material, the addition of graphite nanoparticles with mass concentration of 0.1 % does not significantly affect the charging and discharging times compared to base phase change material. The differences in charging and discharging times did not exceed 11 %. For a graphite nanoparticles mass concentration of 5 %, an increase in the charging time by up to 21 % and a reduction in the discharging time by 24 % was observed, depending on the type of base phase change material. An addition of multi-walled carbon nanotubes with mass concentration of 0.1 % shows an increase in charging time regardless of the type base phase change material up to 144 % with negligible influence on the discharging time. It was also observed that adding a surfactant to the produced nano-enhanced phase change material results in a reduction in charging time by up to 83 % depending on the type of base phase change material.

Stability and thermodynamic property of TiO2/R141b nanorefrigerants by multi‐objective optimization

AbstractUtilizing nanorefrigerants as working fluids can significantly enhance the energy efficiency of low‐temperature waste heat recovery systems (≤ 50°C). Refrigerants with low viscosity and density require a substantial amount of surfactant to maintain a stable suspension of nanoparticles. However, the excessive use of surfactants, which have a notably low thermal conductivity, could lead to foam generation and reduce heat transfer coefficient. High viscosity lubricating oils with small amount of surfactant can prolong the stable suspension time and produce repulsive force. Therefore, a new combination of them improves the stability of TiO2/R141b nanorefrigerants. Additionally, viscosity and thermal conductivity of the nanorefrigerants were optimized using an implementation of a modified non‐dominated sorting genetic algorithm (NSGA‐II). The results show that adding lubricating oil inhibits aggregation of the nanoparticles leading to a stable suspension for more than 6 h at volumetric mixing ratios (lubricating oil: refrigerant) greater than 1:30. The best dispersion stability was achieved at surfactant polyvinyl pyrrolidone (PVP) mass ratio of 0.5, and the average absorbance value was increased by 65.45%. Compared with pure refrigerants, the thermal conductivity of TiO2/R141b (0.15 vol.%) nanorefrigerant was enhanced by up to 12.59% under the optimum mixing ratio. Moreover, the studied nanorefrigerants exhibited shear thickening behavior throughout the studied shear rate range, with increased non‐Newtonianization with decreasing temperature. Finally, the Pareto points were divided into three representative groups based on thermal conductivity and viscosity. These findings suggest enhanced high heat transfer efficiency with pumping power of nanorefrigerant in the waste heat recovery systems.

Controlled Growth of a Highly Energetic, Less Electron-Dense Tetrahedral Fe3+ Phase on the Surface of α-Fe2O3 Nanoparticles toward Enhanced Optical, Magnetic, and Supercapacitive Performance

Nanoplate to pseudocubic-shaped hematite (α-Fe2O3) nanoparticles along with the gradual engravement of tetrahedral Fe3+ has been synthesized by controlling the precursor (FeCl3 ·6H2O) concentration from 0.005 M (A1) to 0.2 M (A4). The role of the surfactant polyvinylpyrrolidone on the preferential plane ([110] to [012]) growth and highly energetic tetrahedral Fe3+ phase (increases 2.7 times for A4 than A1) nucleation over the hematite surface has been elucidated from the HRTEM images, XPS, and Raman spectroscopy. This tetrahedral phase and the morphology variation facilitate the Fe–Fe interaction significantly, which improves the saturation magnetization from 0.13 emu/g (A1) to 0.37 emu/g (A4). Stronger magnetic d–d coupling in the A4 sample promotes dominant photoluminance (PL) spectra. It also exhibits linear dependence with the excitation wavelength (300–380 nm) that can be exploited in the design of a UV detector. The supercapacitive performance of ethylene glycol supported PEDOT-PSS-α-Fe2O3 composite films as negative electrode materials, in the voltage window of −1.3 to −0.5 V, suggests this material to be a promising candidate for the next-generation charge storage devices. The sample engraved with the richest Fe3+ ions shows the highest specific capacitance of 705.7 F/g in 2 M SO32– electrolytes, and its cyclic stability increases to 111% over 1500 cycles.

Gram-scale solvothermal synthesis of Fe-doped CuCoO2 nanosheets and improvement of the oxygen evolution reaction performance.

In this work, we used Cu-BTC-IPA and Co(NO3)2·6H2O as precursors to synthesize CuCoO2 (CCO) nanocrystals with a suitable crystal phase, morphology and high yield by changing the process parameters, such as reactant concentration, reactant ratio, mineralizer dosage, and the type of polyvinylpyrrolidone surfactant. In addition, the effects of different concentrations (1 at%, 3 at%, 5 at%) of Fe doping on the crystal structure and oxygen evolution reaction (OER) performance of CCO were studied. The experimental results show that Fe ions are uniformly doped into the lattice to replace the A-site (Cu+) position, which not only reduces the grain size of CCO, but also increases its specific surface area. We further employed the density functional theory (DFT) method to simulate the OER process of transition metal Fe-doped CCO (A-site substitution) and proposed that Fe doping can reduce the Gibbs free energy of each step and promote the formation of each intermediate, thereby improving its OER catalytic performance. In 1.0 M KOH electrolyte, the 3 at% Fe-doped CCO (Ni@3FCCO) electrode has the best OER performance (η10 = 369 mV, Tafel slope = 69 mV dec-1), and the required overpotential to attain 10 mA cm-2 slightly increased (∼30.2 mV) after 18 hours of continuous OER. The crystal morphology and chemical composition did not change significantly before and after the long-term OER test, indicating that the 3FCCO nanosheets have good OER activity and stability. We have proposed two reasons for the significant improvement of OER performance for Fe-doped CCO nanosheets: (1) the partial substitution of Cu cations by Fe cations not only regulates the electronic structure of CCO, making the catalytically active center no longer a single Co site, but also contains the Fe site, thus increasing the number of overall active sites; (2) the synergistic effect between Fe cations and Co cations in the OER process could enhance the activity of a single active site.

The synthesis of bismuth telluride nanowires with a high aspect ratio via precise regulation of growth rates

It is challenging to obtain one-dimensional nanowires with a high aspect ratio. Herein, we developed a controllable hydrothermal method to synthesize single-crystalline bismuth telluride (Bi2Te3) nanowires with a high aspect ratio. The effects of growth conditions including template, temperature, surfactant polyvinyl pyrrolidone (PVP) dosage, and pH value on the aspect ratio of Bi2Te3 nanowires were studied. The results show that Te nanowire templates not only support the epitaxial growth but also supply the Te source of Bi2Te3 nanowires. The reaction temperature, surfactant PVP, and pH were carried out to adjust the nucleation and diffusion rates of Bi and Te, thus controlling the growth rates of Bi2Te3 nanowires. The obtained Bi2Te3 nanowires have an aspect ratio of up to 100 (length of 7 µm and width of 70 nm).

Effect of sintering optimization on the photoelectrochemical performance of Cu2ZnSnS4 nanocrystal films

AbstractBACKGROUNDSemiconductor‐based photoelectrochemical (PEC) water splitting represents one attractive route to generate clean hydrogen. Cu2ZnSnS4 (CZTS) is considered a promising photoelectric material for PEC water splitting due to its high absorption coefficient, small bandgap, nontoxicity, and earth‐abundant elements. Only a few critical parameters limit the performance of CZTS nanocrystal films. Of those, heat treatment is essential for producing high‐performance films.RESULTSIn this work, CZTS nanocrystals were produced by a facile method and applied in making CZTS films for PEC water reduction. Therefore, the influences of heat treatment parameters on the performance of films were investigated in the low‐temperature heat treatment range. The surfactant polyvinylpyrrolidone (PVP) in the films could not be completely decomposed at low heat treatment temperatures, leading to film resistance that was harmful to the PEC process. Meanwhile, SnSx impurities would arise at temperatures over 400 °C, thus reducing the PEC performance.CONCLUSIONThe best activity for PEC water reduction was obtained at 385 °C for 10 min. Furthermore, the PEC performance of CZTS films generated by fast heating (10 °C s−1) was superior to that of films generated by slow heating (10 °C min−1) due to the inhibition from the development of SnSx impurities. © 2022 Society of Chemical Industry (SCI).

Effect of light at different wavelengths on polyol synthesis of silver nanocubes

Despite the presence of light-sensitive species in the polyol synthesis of silver nanocubes, the influence of light on it has yet to be investigated. Herein, we demonstrated that light radiation, by generating plasmon-based hot electrons and subsequently increasing the reduction rate of Ag+ in the system, in addition to enhancing the growth rate of nanocubes, causes twinned seeds, which these seeds are then converted into nanorods and right bipyramids. With shorter, higher energy wavelengths, Ag+ reduction progresses more quickly, resulting in structures with more twin planes. The overlap of the excitation wavelength and the band gap of Ag2S clusters formed in the early stages of synthesis accelerates the rate of reaction at low-energy excitation. According to our findings, the surfactant polyvinylpyrrolidone acts as a photochemical relay to drive the growth of silver nanoparticles. Overall, this work emphasizes the impact of excitation light on polyol synthesis as a technique for generating Ag nanocubes of various sizes.

Rheology and thermal conductivity of graphene oxide and coal fly ash hybrid nanofluids for various particle mixture ratios for heat transfer applications: Experimental study

This work presents the synthesis of graphene oxide (GO) and coal fly ash (CFA) nanoparticles (NP) to produce water base mono and hybrid nanofluids (HNF) for different particle mixture ratios of 50:50 and 30:70. X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), dynamic light scattering analysis (DLS), Fourier transform infrared (FTIR), field emission scanning electron microscope (FESEM), Ultraviolet-visible spectroscopy analysis (UV–Vis), and zeta-potential tests were carried out. The non-ionic surfactant polyvinylpyrrolidone (PVP) is added to the nanofluid (NF) to improve stability. The thermal conductivity (TC) and rheology experiments are carried out for the concentration range of 0.1 to 1.0 vol% in the temperature range of 30 to 60 °C. The results show that TC and viscosity (VST) enhancement of GO NF is higher than the studied HNF. The maximum VST enhancement of 177%, 152%, and 113% are observed for GO, and GO/CFA (50:50) and, GO/CFA (30:70), respectively for a concentration of 1 vol% at 30°C relative to water. Based on the obtained data, regression analysis is formed to estimate the TC and VST of the studied HNF. The performance enhancement ratio (PER) results show that GO NF and HNF with a mixture ratio of 30:70 are beneficial for thermal applications at all temperatures, whereas HNF with a mixture ratio of 50:50 is only at 45°C and above.

PVP-assisted hydrothermal synthesis of rod-like NiCo2O4 powders as high-performance microwave absorbers

Rod-like NiCo2O4 powders were synthesized by hydrothermal method in the presence of polyvinylpyrrolidone (PVP) surfactant for absorption the microwaves (1–18 GHz). The structural, microstructural, magnetic, and electromagnetic properties were analyzed by various characterization techniques. By adding the PVP surfactant, the wood-like texture morphology was transformed to the rod-like morphology composed of spherical nanoparticles (∼15 nm). The single-phase NiCo2O4 obtained by PVP agent had the higher crystallinity and oxygen vacancies in compared with the wood-like texture NiCo2O4 morphology. The specific surface area and pore volume decreased from 83 to 65 m2/g and from 0.13 to 0.05 cm3/g by using PVP agent, respectively. The rod-like NiCo2O4 powders exhibited the wider effective absorption band of ∼4.9 GHz in the Ku (12–18 GHz) band at a matching thickness of 1.4 mm in comparison with 3.9 GHz for the wood-like NiCo2O4 powders at the matching thickness of 1.2 mm. The better microwave absorption performance of the rod-like NiCo2O4 powders was attributed to their good impedance matching caused by their lower permittivity and higher permeability.

Enhanced Methylene Blue Adsorption by Cu-BTC Metal-Organic Frameworks with Engineered Particle Size Using Surfactant Modulators

Metal–organic frameworks (MOFs) featuring porous structures and large specific surface areas have shown great potential in removing organic pollutants from wastewater via adsorption processes. Although the particle size of MOFs determines the adsorption performance (something known as the size-dependent effect), engineering it into desirable dimensions for enhancing the adsorption performance is a great challenge. Here, we develop a practical and facile approach to regulate the particle size of copper benzene-1,3,5-tricarboxylate (Cu-BTC) adsorbents with high tunability by screening the functional modulator of various surfactants adding in hydrothermal synthesis procedure. The effect of surfactant type and concentration on the particle size of Cu-BTC was systematically investigated. The results show that the nonionic surfactant polyvinylpyrrolidone (PVP) demonstrated the greatest ability to control the particle size of Cu-BTC among other counterparts (e.g., N, N, N-trimethyl-1-dodecanaminium bromide (DTAB), polyethylene glycol (PEG1000), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and hexadecyl trimethyl ammonium bromide (CTAB)). By increasing the PVP concentration to 0.14 mmol L−1, the average particle size of Cu-BTC could be correspondingly reduced by more than ten times, reaching to a comparative smaller value of 2.4 μm as compared with the reported counterparts. In addition, the PVP allowed a large increase of the surface area of Cu-BTC according to porosity analysis, resulting in a great enhancement of methylene blue (MB) adsorption. The PVP-modulated Cu-BTC showed fast adsorption kinetics for MB removal accompanied with a maximum adsorption capacity of 169.2 mg g−1, which was considerably competitive with most of the analogs reported. Therefore, our study may inspire concepts for engineering the particle size of Cu-BTCs with improved properties for more practical applications.

Boosting the active sites and kinetics of VO2 by Mn pre-intercalated and PVP modified nanostructure to improve the cycle stability for aqueous zinc batteries

The VO 2 after Mn-doped and PVP-modified as aqueous zinc ion battery cathode materials. Both embedding of Mn and the modification of PVP can improve the morphology and internal structure of the material to improve performance. • Mn-doped and PVP-modified VO 2 as cathode materials for aqueous zinc battery. • Surfactant PVP significantly improves the morphology of the material. • The insertion of Mn ions boosts the internal structure and stability. • Dual engineering strategy of intercalation and morphology improvement. Aqueous zinc ion batteries (ZIBs) have attracted extensive attention because of its high cost-performance and high safety. This study reports a structural engineering method that embeds Mn ions as pillars into the VO 2 layered structure, and improves the morphology through polyvinylpyrrolidone (PVP) to increase the specific surface area, thereby obtaining MnVO 2 -PVP. Increasing the number of electrochemically active sites allows it to have faster ion diffusion kinetics and better long-term cycle stability. The synthesized MnVO 2 -PVP with nanoprism and nanosheet composite structure shows a remarkable capacity of 470.2 mAh g −1 at 0.5 A g −1 , and also has excellent cycle stability at 5000 times at 10 A g −1 . The capacity after cycling is 176.5 mAh g −1 , with high energy density (179 W h kg −1 ) and power density (7000 W kg −1 ). The synthesis method and marvelous performance of MnVO 2 -PVP can lay a foundation for the improvement of the synthesis method of ZIBs cathode materials in the future.

Eco-Friendly Synthesis of Silver Nanoparticles Using Pulsed Plasma in Liquid: Effect of Surfactants

Silver (Ag) nanoparticles were successfully prepared by using the in-liquid pulsed plasma technique. This method is based on a low voltage, pulsed spark discharge in a dielectric liquid. We explore the effect of the protecting ligands, specifically Cetyl Trimethylammonium Bromide (CTAB), Polyvinylpyrrolidone (PVP), and Sodium n-Dodecyl Sulphate (SDS), used as surfactant materials to prevent nanoparticle aggregation. The X-Ray Diffraction (XRD) patterns of the samples confirm the face-centered cubic crystalline structure of Ag nanoparticles with the presence of Ag2O skin. Scanning Transmission Electron Microscopy (STEM) reveals that spherically shaped Ag nanoparticles with a diameter of 2.2 ± 0.8 nm were synthesised in aqueous solution with PVP surfactant. Similarly, silver nanoparticles with a peak diameter of 1.9 ± 0.4 nm were obtained with SDS surfactant. A broad size distribution was found in the case of CTAB surfactant.

Effect of surfactants on the stability, rheological properties, and thermal conductivity of Fe3O4 nanofluids

Stability is the major factor that enables the application of nanofluids in energy conversion systems. Excellent rheological and thermal conductivity is the key for nanofluids to be an ideal heat transfer medium. In this work, we investigated the stability of Fe3O4 nanofluids by four characterization techniques, mainly from the viewpoint of surfactant type and mass ratio, and systematically studied its rheological and thermal conductivity properties by different experimental methods and analyzed the behavior of magnetic fluid thermal anisotropy by mathematical methods. The experimental results show that the surfactant Tetramethylammonium hydroxide (TMAH) has the best stability effect and can keep the Fe3O4 nanofluids more than 120 h. And the best ratio is when the mass ratio of Fe3O4 to TMAH is 1:4. The surfactant Polyvinylpyrrolidone (PVP) has the greatest effect on nanofluids viscosity. The increase in TMAH mass leads to a Newtonian fluid behavior of the nanofluids at low temperatures and low shear rates, besides shifting its shear thinning towards the high temperature region. However, from the curve relationship between the shear rate and shear stress, the Fe3O4 nanofluids belongs to the expansion fluid among non-Newtonian fluids. The surfactant Sodium dodecyl sulfate (SDS) have the greatest effect on the thermal conductivity of Fe3O4 nanofluids. Theoretical calculations show that as the concentration increases, the rate of heat transfer in the direction of the parallel magnetic field is significantly greater than in the direction of the perpendicular magnetic field, while the rate of heat transfer in the absence of a magnetic field is somewhere in between.

Experimental Performance Evaluation and Artificial-Neural-Network Modeling of ZnO-CuO/EG-W Hybrid Nanofluids

The thermo-physical properties of nanofluids are highly dependent on the used base fluid. This study explores the influence of the mixing ratio on the thermal conductivity and viscosity of ZnO-CuO/EG (ethylene glycol)-W (water) hybrid nanofluids with mass concentration and temperatures in the ranges 1-5 wt.% and 25-60°C, respectively. The characteristics and stability of these mixtures were estimated by TEM (transmission electron microscopy), visual observation, and absorbance tests. The results show that 120 min of sonication and the addition of PVP (polyvinyl pyrrolidone) surfactant can prevent sedimentation for a period reaching up to 20 days. The increase of EG (ethylene glycol) in the base fluid leads to low thermal conductivity and high viscosity. Thermal conductivity enhancement (TCE) decreases from 21.52% to 11.7% when EG:W is changed from 20:80 to 80:20 at 1 wt.% and 60°C. A lower viscosity of the base fluid influences more significantly the TCE of the nanofluid. An Artificial Neural Network (ANN) has also been used to describe the effectiveness of these hybrid nanofluids as heat transfer fluids. The optimal number of layers and neurons in these models have been found to be 1 and 5 for viscosity, and 1 and 7 for thermal conductivity. The corresponding coefficient of determination (R2) was 0.9979 and 0.9989, respectively.

Layered double (Ni, Fe) hydroxide grown on nickel foam and modified by nickel carbonyl powder and carbon black as an efficient electrode for water splitting

Developing novel oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts is vital for water splitting. Here, carbon black (CB) and nickel carbonyl powder (NCP) are used as components, and the nonionic surfactant polyvinyl pyrrolidone (PVP) is used as a shape-controlled capping agent to easily prepare layered double (Ni, Fe) hydroxide (NiFe-LDH) electrodes. Scanning electron microscopy observation and X-ray photoelectron spectra analysis show that the Fe2+-doped layered double hydroxide is grown in situ on nickel foam (NF). CB (XC-72) and NCP further improve the electrical conductivity. At 10 mA•cm−2, the overpotentials of the OER and HER are 203 mV and 83 mV, respectively, in 1 M KOH. Only 1.48 V is needed when both electrodes are applied for water splitting, and it has a stability of more than 100 h. This work can be used as a medium to elevate the OER and HER performance of NiFe-LDH-based catalysts.

Water-based graphene/AgNPs hybrid conductive inks for flexible electronic applications

Currently, inkjet printing of the hybrid conductive inks plays a critical role in the technological advancement to fabricate flexible electronics. In this study, flexible electronics based on water-based graphene, silver nanoparticles (AgNPs), and graphene/AgNPs hybrid printed on polyethylene terephthalate substrate (PET) substrate were developed. The properties of the conductive inks were evaluated based on different concentrations of polyvinylpyrrolidone (PVP) surfactants (0.1, 0.3, 0.5, and 0.7 wt%). Among the conductive ink formulations, G/AgNPs hybrid inks fabricated with 0.5 wt% PVP surfactant exhibited better stability, wettability, and electrical conductivity. Moreover, the electrical conductivity of G/AgNPs hybrid conductive traces performed more than 100 times higher than G and AgNPs conductive traces. In addition, it was observed that under 50% tensile and 100 bending times, the printed hybrid conductive traces exhibited only 4% and 3% drop in conductivity, respectively. Therefore, conductive inks prepared from water-based G/AgNPs hybrid ink are thought to be appropriate for usage in printed flexible electronic applications.

Surfactant assisted dispersion of graphene in aqueous solution using mixed surfactants

In this work, graphene is initially dispersed in surfactant sodium dodecyl sulfonate (SDBS) in an aqueous solution. Sonication followed by centrifugation is the process used to disperse the graphene in an aqueous solution with the aid of SDBS. The concentration of graphene is determined using UV–Vis-NIR spectroscopy. A higher concentration of graphene is achieved just above the critical micelle concentration of SDBS in an aqueous solution. To further improve the concentration of graphene in an aqueous solution of SDBS, a second surfactant polyvinyl pyrrolidone (PVP) is used. The mixed surfactant strategy has increased the concentration of graphene in an aqueous solution by ∼ 400% as compared to SDBS aided dispersion of graphene in an aqueous solution. Atomic force microscopy (AFM) observations reveal the few-layer dispersion of graphene in an aqueous solution with the aid of mixed surfactants; while SDBS assisted dispersion of graphene in an aqueous solution shows the few layers to 10 s of layers of graphene nanosheets.

Surface controlled synthesis of Cu2FeSnS4 particles for enhanced hydrogen evolution reaction

Cu2FeSnS4 (CFTS) particles are synthesized using different surfactants such as thioglycolic acid (TGA), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) via the solution process. The effect of surfactants on crystal structure, morphology, elemental composition, and electrocatalytic properties of CFTS particles are investigated. CFTS particles with a better crystalline phase are obtained in PVP (surfactant), while impurity phases are observed in TGA and PVA (surfactants). The morphology of CFTS is significantly changed when a different surfactant is used in the synthesis process. The mixture of aggregate and porous (1 μm) particles is observed when PVA is used as a surfactant to synthesize CFTS particles. At the same time, highly porous particles having nanosheets and nanoparticles at the surface are obtained in the case of PVP. In the TGA case, spherical particles with 1 μm size are observed. The electrocatalytic ability of all CFTS particles toward hydrogen evolution reactions (HER) is studied in 0.5 M H2SO4 electrolyte. The overpotential of PVP-based CFTS particles is the lowest as ƞ = 421 mV at 10 mA/cm2 compared to the other two samples. CFTS particles synthesized using PVP exhibit enhanced electro-catalytic performance due to higher surface area.