Biosorption was carried out in this study using the biomass of microalgae Scenedesmus sp. as adsorbent for the removal of hexavalent chromium or Cr(VI) from solution. Different relevant parameters ...like initial pH, contact time, initial Cr(VI) concentration, biosorbent dosage, particle size, and temperature were examined to evaluate their effect. They were found to be effective with the maximum of 92.89% Cr loading onto the biomass. The FTIR analysis revealed the presence of easily hydrolyzed functional groups like aldehydes, amides, carboxylic acids, phosphates, and halides, which charged positively below the point of zero charge at pH 2.65. The biosorption proceeded through the anionic adsorption mechanism and followed the pseudo-first order kinetic model. Its feasibility was confirmed as the experimental data closely fitted to both Langmuir and Freundlich isotherms. The biosorption was spontaneous. Its spontaneity increased with the increase of temperature. The positive entropy change suggested the randomness at the solid-liquid interface. This study recommended that the toxic Cr(VI) could be removed from different contaminated water samples in the nearby chromite mines using the microalgae biomass. However, it requires attention in some other sides like activation of biomass, interference of other ions, elevation of the experimental pH, the large biomass generation and harvesting, desorption of the Cr-loaded biomass, and recovery of the energy value of the waste biomass.
Herein, we report the synthesis of metal (Pt and Au) and metal alloy (PtAu) nanoparticles (NPs)-integrated graphitic carbon nitride (g-C3N4) hybrids using a facile solvothermal route for ...water-splitting application. The metal and metal alloy NPs with varying percentages of Pt and Au are found to be in the size range of 3–5 nm and uniformly distributed on the g-C3N4 sheets. The metal and metal alloy NPs act as cocatalyst for g-C3N4 to enhance the photocatalytic activity for hydrogen (H2) generation through higher light absorption and efficient charge separation. The alloy composition plays an important role to maximize the photoactivity, with an optimized PtAu/g-C3N4 sample delivered 1009 μmol g–1 h–1 of H2. The visible light assisted photocatalytic H2 evolution is further investigated with the optimized PtAu alloy NPs-integrated g-C3N4. This study presents a robust, stable, and easily synthesizable PtAu/g-C3N4 hybrid material as a promising photocatalyst for H2 generation through water splitting.
In this study, we demonstrate the systematic shape evolution of Cu2O crystals from the octahedron, through truncated octahedron, cube, and finally to truncated cube by varying the reaction ...temperature with an optimum precursor concentration of 25 mM Cu(NO3)2·3H2O and 1 g of polyvinylpyrrolidone (PVP) as the shape controlling reagent. The average size of these crystals increased with temperature from ∼70 nm (at 40 °C) to ∼1 μm (at 100 °C). With a much lower (6 mM) and higher (250 mM) precursor concentration, nanoparticles and polyhedron-shaped crystals are respectively formed in the studied temperature region (40–120 °C). The role of precursor concentration, PVP quantity, reaction medium, and reaction temperature in the formation of diverse Cu2O crystals morphologies are demonstrated and discussed. Furthermore, the catalytic activity of the as-synthesized Cu2O crystals is tested for the reduction of Cr(VI) at room temperature. The toxic Cr(VI) is found to be rapidly reduced to nontoxic Cr(III) in a short span of 4 min in the presence of Cu2O cubes in the acidic medium. The repeat catalytic measurements of Cr(VI) reduction for 20 cycles confirm higher stability of cube-shaped Cu2O crystals with {100} exposed facets as compared to octahedrons with {111} exposed facets, a classic example of facets-dependent catalytic properties of crystals.
Hexavalent chromium (Cr(VI)) in water is a proven carcinogen to different internal and external organs of the living organisms. There are different human activities incorporated to the anthropogenic ...sources in the environment enriching Cr(VI) of high concentration in the water system above the regulatory level. The physical, chemical and biological properties of chromium favour the dissolution in the water environment. This concerns the environmental researcher to tackle and mitigate. Chemical or biological techniques or a combination of the two have been used to remove Cr(VI) from polluted waters. Biological techniques include integrated bioremediation, such as the primary processes of direct bioreduction and biosorption, and secondary processes of microbial fuel cell, biostimulation, surface modified dry biomass and biochar adsorption, and engineered biofilm and cell free reductase. These techniques are used by a wide range of living organisms including bacteria, fungi, plants, plant leaves, plant nuts and algae. This group of living organisms transform and remove Cr(VI) from water during the cellular metabolisms, extracellular activities, physical and chemical adsorptions on the cell surface, and photosynthesis. Variation of different physical, chemical and environmental parameters affecting the efficiency of the bioremediation process have impacted on the design of bioreactors. There has been a recent development of a microbial fuel cell which use the proximity of Cr(VI) reduction as a cathode half cell for the generation of renewable energy and simulation of its’ removal from water.
Development of active materials capable of delivering high specific capacitance is one of the present challenges in supercapacitor applications. Herein, we report a facile and green solvothermal ...approach to synthesize graphene supported tungsten oxide (WO3) nanowires as an active electrode material. As an active electrode material, the graphene–WO3 nanowire nanocomposite with an optimized weight ratio has shown excellent electrochemical performance with a specific capacitance of 465 F g–1 at 1 A g–1 and a good cycling stability of 97.7% specific capacitance retention after 2000 cycles in 0.1 M H2SO4 electrolyte. Furthermore, a solid-state asymmetric supercapacitor (ASC) was fabricated by pairing a graphene–WO3 nanowire nanocomposite as a negative electrode and activated carbon as a positive electrode. The device has delivered an energy density of 26.7 W h kg–1 at 6 kW kg–1 power density, and it could retain 25 W h kg–1 at 6 kW kg–1 power density after 4000 cycles. The high energy density and excellent capacity retention obtained using a graphene–WO3 nanowire nanocomposite demonstrate that it could be a promising material for the practical application in energy storage devices.
A simple electrochemical deposition technique is used to deposit ZnO nanostructures with diverse morphology directly on ITO-coated glass substrates at 70 °C. The concentration of the Zn(NO3)2·6H2O ...electrolyte is important to controlling the dimensionality of the nanostructures, with formation of one-dimensional (1D) nanospikes and nanopillars (with 50−500 nm diameter) below 0.01 M and of two-dimensional (2D) nanowalls and nanodisks (with 50−100 nm wall/disk thickness) above 0.05 M. Glancing-incidence X-ray diffraction study shows their wurtzite structure and confirms the change in the preferred crystal plane orientation with the dimensionality of ZnO nanostructures. UV−vis spectroscopy reveals a higher transmittance from 2D nanostructures than from 1D nanostructures and their optical direct band gaps estimated to be 3.12−3.27 eV. Depth-profiling X-ray photoemission studies show the presence of Zn(OH)2 outer layers on the ZnO nanostructures, with a higher Zn(OH)2 moiety for 2D nanostructures relative to 1D nanostructures. Furthermore, a substantial quantity of Cl (provided by the KCl supporting electrolyte) is detected throughout the 2D nanostructures only. The photoemission data therefore affirm our proposed growth mechanism that involves capping of the preferred 0001 growth direction by Cl− ions under fast hydroxylation kinetics condition as observed at a higher Zn(NO3)2·6H2O electrolyte concentration.
Microbial fuel cells (MFCs) are emerging as a sustainable technology for waste to energy conversion where electrode materials play a vital role on its performance. Platinum (Pt) is the most common ...material used as cathode catalyst in the MFCs. However, the high cost and low earth abundance associated with Pt prompt the researcher to explore inexpensive catalysts. The present study demonstrates a noble metal-free MFC using a manganese ferrite (MnFe2O4)/polyaniline (PANI)-based electrode material. The MnFe2O4 nanoparticles (NPs) and MnFe2O4 NPs/PANI hybrid composite not only exhibited superior oxygen reduction reaction (ORR) activity for the air cathode but also enhanced anode half-cell potential upon modifying carbon cloth anode in the single-chambered MFC. This is attributed to the improved extracellular electron transfer of exoelectrogens due to Fe3+ in MnFe2O4 and its capacitive nature. The present work demonstrates for the first time the dual property of MnFe2O4 NPs/PANI, i.e., as cathode catalyst and an anode modifier, thereby promising cost-effective MFCs for practical applications.
Metal-free catalysis for electrocatalytic hydrogen evolution from water is very demanding for the production of sustainable and clean fuel. Herein, we report the synthesis of a porphyrin-based ...metal-free covalent organic polymer (TpPAM) through a simple condensation between triformyl phloroglucinol (Tp) and 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin (PAM). The as-prepared porous TpPAM exhibited superior activity for the hydrogen evolution reaction (HER) current density of 10 mA cm–2 at a low overpotential of 250 mV and a small Tafel slope of 106 mV decade–1, which are better than those of related metal-free electrocatalysts. The high HER activity of TpPAM was investigated in-depth via theoretical density functional theory (DFT) calculations. The theoretical findings were correlated with the experimental results, and these were in good agreement for high HER catalytic efficiency of the porous TpPAM polymer. The Faradaic efficiency of the TpPAM-based electrode was found to be 98%, which is very close to the ideal value of 100%, reflecting its potential for practical implementation. Moreover, the as-synthesized catalyst showed good stability by retaining 91% of the initial current density after 1000 cycles.
Electrochemical oxygen evolution reaction (OER) involves high overpotential at the oxygen evolving electrode and thereby suffers significant energy loss in the proton exchange membrane water ...electrolyzer. To reduce the OER overpotential, precious ruthenium and iridium oxides are most commonly used as anode electrocatalyst. Here we report marked reduction in overpotential for the OER using transition metal (TM) doped TiO2 nanocrystals (NCs). This reduction in overpotential is attributed to d-orbitals splitting of the doped TMs in the TM-doped TiO2 NCs and their interactions with the oxyradicals (intermediates of OER) facilitating the OER. The d-orbital spitting of TMs in TM-doped TiO2 NCs is evident from the change in original pearl white color of undoped TiO2 NCs and UV–vis absorption spectra.
Aluminum was electrodeposited from two different ionic liquid electrolytes namely; 1-ethyl-3-methylimidazolicum chloride and AlCl3 (EMIC–AlCl3) and 1-butyl-3-methylimidazolium chloride (BMIC–AlCl3) ...at 90 ± 2 °C. Nodular morphology of aluminum was obtained at the copper substrate. To evaluate the reaction mechanism, chronoamperometric study was adopted. From the chronoamperometric analysis, it was observed that the reaction was controlled by instantaneous three-dimensional diffusion process. The diffusion coefficient (D) of Al2C7− was found to be 5.2–6.6 × 10−11 m2 s−1 and 2.2 × 10−11 m2 s−1 for EMIC–AlCl3 and BMIC–AlCl3 ionic liquid electrolytes, respectively. The nuclei density of electrodeposited aluminum on the copper was also confirmed by scanning electron microscope wherein uniformly distributed aluminum nodules were observed.
•Al electrodeposit was obtained using EMIC–AlCl3 and BMIC–AlCl3 ionic liquids.•Deposition process was governed by instantaneous 3-dimensional nucleation.•Diffusion coefficient was found in the order of 10−11 m2 s−1 for both electrolytes.•Number of nuclei sites of aluminum was estimated in the order of 1012 N m−2.
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