Alkaline Solution Research Articles

An integrated approach to sustainable mine wastewater treatment: Magnesium recovery with anion exchange membranes

With recent emphasis on sustainable and efficient mineral valorization, novel approaches to treating mineral wastewater in natural settings bring both environmental and economic value. This paper presents the results of an applied research to develop an integrated approach to sustainable wastewater treatment that includes an ion exchange process to recover copper and cobalt from mine wastewater, followed by the membrane recovery of magnesium. The paper investigates magnesium hydroxide crystallization process employing an anion exchange membrane (AEM) cell. This process involves the penetration of OH- ions from the alkaline solution through the AEM to the feed solution in exchange for Cl- ions and precipitation of Mg(OH)2 as solid particles. The wastewater was sampled from different mine waste sources from the copper mine tailings dam in South Australia, all containing significant amounts of critical metals, including magnesium, copper, and cobalt. The results have demonstrated the potential for sustainable magnesium hydroxide recovery methods. The findings suggest that the most influential process parameters for magnesium hydroxide recovery and purity are magnesium concentration in the feed solution and sodium hydroxide to magnesium ratio in the alkaline solution and feed solution, respectively. It was also established that the overall recovery of cobalt, copper and magnesium in a combination of ion exchange and AEM processes was achieved at a level near 100 %. The purity of magnesium hydroxide precipitate was achieved in the range of 90–96.6 % and depends mainly on the presence of impurities in brine.

Antimicrobial Activity of Amino-Modified Cellulose Nanofibrils Decorated with Silver Nanoparticles.

Silver nanoparticles (Ag NPs) conjugated with amino-functionalized cellulose nanofibrils (NH2-CNFs) were in situ-prepared by reducing silver ions with free amino groups from NH2-CNFs. The spectroscopy and transmission electron microscopy measurements confirmed the presence of non-agglomerated nanometer-in-size Ag NPs within micrometer-large NH2-CNFs of high (20 wt.-%) content. Although the consumption of amino groups during the formation of Ag NPs lowers the ζ-potential and surface charge of prepared inorganic-organic hybrids (from +31.3 to +19.9 mV and from 2.4 to 1.0 mmol/g at pH 7, respectively), their values are sufficiently positive to ensure electrostatic interaction with negatively charged cell walls of pathogens in acidic and slightly (up to pH ~8.5) alkaline solutions. The antimicrobial activity of hybrid microparticles against various pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) is comparable with pristine NH2-CNFs. However, a long-timescale use of hybrids ensures the slow and controlled release of Ag+ ions to surrounding media (less than 1.0 wt.-% for one month).

From kitchen to cosmetics: Study on the physicochemical and antioxidant properties of waste cooking oil-derived soap

A large amount of used cooking oil (UCO) is improperly disposed of in sewage and rivers, leading to environmental pollution and posing health risks such as carcinogenic diseases. This study explores an eco-friendly approach to addressing this issue by repurposing UCO for laundry soap production, contributing to waste management and environmental decontamination. The soap was prepared by treating UCO with an alkaline solution (NaOH) through a simple saponification process, providing a greener alternative to traditional methods that rely on imported vegetable oils. The prepared soaps were evaluated for cleansing capacity as well as physical, chemical, and physicochemical properties. The results showed moisture content of 9.27 % to 10.34 %, pH ranging from 6.03 to 4.46, chloride percentage from 0.055 % to 0.29 %, free caustic alkali between 0.152 and 0.175, and total alkali content from 0.29 % to 0.73 %. These values meet the requirements of East African Standards (EAS), validating the quality of UCO-based soaps. By diverting UCO from waste streams and utilizing it in soap production, this approach supports waste management, minimizes environmental pollution, and contributes to sustainable production practices.

Ionising and ultraviolet radiation induce the secretion of melanin in Tetrahymena pyriformis

ABSTRACT The objective of this study was to determine the effect of ionising and ultraviolet radiation on stimulating melanin secretion in Tetrahymena pyriformis. Cell cultures were exposed to different doses of radiation for 48, 72 and 96 h. After incubation, melanin was extracted and analysed. Our results showed that melanin concentration increased with increasing irradiation dose and exposure duration. Melanin was insoluble in water and organic solvents but soluble in alkaline and acidic solutions. A linear correlation between the logarithm of melanin absorbance and wavelength ranging from 400 to 600 nm was observed. The HPLC chromatograms of melanin degradation products by the alkaline hydrogen peroxide oxidation method revealed the existence of four peaks. The natural melanin standard extracted from the cuttlefish Sepia officinalis was used as a reference compound of eumelanin markers. These markers were detected in control cells, irradiated cells and black human hair but with different intensities.

Pepgen-P15 delivery to bone: A novel 3D printed scaffold for enhanced bone regeneration

Pepgen-P15 is a combination of an organic hydroxyapatite matrix derived from bovine sources, combined with a synthetic peptide known as P-15. The interaction between α2β1 integrin and the P15 chain triggers both intracellular and extracellular signaling pathways, resulting in the production of growth factors. Three-dimensional (3D) printing has recently emerged as an innovative strategy for developing personalized therapies in bone tissue regeneration. In this research, various ratios of calcium magnesium silicate (bredigite) nanoparticles were used to modify 3D printed scaffolds made of xanthan gum and polycaprolactone (PCL) via fused deposition modeling (FDM). Scaffolds were subsequently treated with an alkaline solution, covered with graphene oxide, and finally, Pepgen-P15 was applied. the effects of xanthan gum were assessed using swellability and contact angle tests. The results indicated that, the prepared scaffolds exhibited suitable degradation rates, mechanical characteristics, and apatite formation. Alizarin red and alkaline phosphatase assays were also conducted to evaluate the scaffolds’ effectiveness in promoting bone cell differentiation during cell culture. Furthermore, the surface of the scaffold was examined to determine the amount of Pepgen-P15 loaded and released. According to the findings, the scaffold composed of 20 % bredigite and 0.3 % graphene oxide, coated with Pepgen-P15, demonstrate optimal mechanical properties, cell adherence, development, and proliferation. Typically, it is a good candidate for use in bone tissue engineering.

Al-etching-induced defect engineering in NiAl LDHs for promoting multifunctional electrocatalytic oxidations: Water oxidation and urea oxidation

Electrocatalytic water splitting is a promising avenue to produce green hydrogen for future sustainable development. Developing multifunctional catalysts with high-performance toward urea oxidation reaction (UOR) and oxygen evolution reaction (OER) offers a unique approach for simultaneously achieving the degradation of urea-containing wastewater and energy-saving hydrogen production. Ni-based materials are a kind of promising materials for electrocatalysis, since its abundant reserve and tolerance. However, low intrinsic activity and catalytic efficiency hinder its wide application. Here, a defect engineering strategy is developed to create vacancies on NiAl layer double hydroxides (LDHs) catalysts by selectively etching Al ions in strong alkaline solution. The obtained NiAl LDHs with rich defects (D-NiAl LDHs) exhibit good OER performance with overpotential of 264 mV to achieve a current density of 10 mA cm−2 and a Tafel slope of 39.8 mV dec−1. In addition, the D-NiAl LDHs catalysts also show excellent UOR activity using a potential of 1.328 V vs. RHE @ 10 mA cm−2 in alkaline solution. In comparation to NiAl LDHs, the enhanced performance of D-NiAl LDHs toward oxidation of small-molecule OH− and urea could be attributed to electronic regulation of defects and a larger electrochemical surface area. Partially replacing the OER with the UOR, the driving voltage of overall water splitting reduces effectively from 1.856 V to 1.688 V at a current of 100 mA cm−2.

Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis.

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

The application of Xinjiang safflower extract on Aidelaisi silk fabric

Purpose This study aims to explore the traditional plant dyeing of Xinjiang Atlas silk fabrics, providing references for the comprehensive utilization of plant dyes in intangible cultural heritage.Design/methodology/approach The focus of this study is on dyeing experiments of Atlas silk fabrics using safflower extracts, constrained by regional resources. Safflower dry flowers grown in Xinjiang were selected, rinsed with pure water and rubbed. Yellow pigments were removed by adding edible white vinegar. Red pigments from safflower were extracted using an alkaline solution prepared with Populus euphratica ash, a special product of Xinjiang. The extraction rate was analyzed under varying material-to-liquor ratios, pH values, times and temperatures. Direct dyeing process experiments were conducted to obtain different colorimetric L, a, b and K/S values for comparison. Samples with good color development were selected to test the impact of dyeing immersions on color development, and their color fastness, UV protection and antibacterial effects were verified.FindingsThe dyeing experiments on silk fabrics confirmed their UV protection capabilities and antibacterial properties, demonstrating effectiveness against E. coli and Staphylococcus aureus. As a major producer of safflower, Xinjiang underscores the significance of safflower as an essential plant dyes on the Silk Road. This study reveals its market potential and suitability for use in the plant dyeing process of Atlas silk, producing vibrant red and pink colors.Originality/valueThe experiments indicated that after removing yellow pigments, the highest extraction rate of red pigment from safflower was achieved at a pH value of 10–11, a temperature of 30°C and an extraction time of 40 min. The best bright red color effect with strong color fastness was obtained with a material-to-liquor ratio of 1:20, a temperature of 40°C and three immersions. The best light pink color effect with strong color fastness was a material-to-liquor ratio of 1:80, a temperature of 30°C and two immersions.

N-ZrS3/p-ZrOS Photoanodes with NiOOH/FeOOH Oxygen Evolution Catalysts for Photoelectrochemical Water Oxidation.

Photoelectrochemical water splitting offers a promising approach for carbon neutrality, but its commercial prospects are still hampered by a lack of efficient and stable photoelectrodes with earth-abundant materials. Here, we report a strategy to construct an efficient photoanode with a coaxial nanobelt structure, comprising a buried-ZrS3/ZrOS n-p junction, for photoelectrochemical water splitting. The p-type ZrOS layer, formed on the surface of the n-type ZrS3 nanobelt through a pulsed-ozone-treatment method, acts as a hole collection layer for hole extraction and a protective layer to shield the photoanode from photocorrosion. The resulting ZrS3/ZrOS photoanode exhibits light harvesting with good photo-to-current efficiencies across the whole visible region to over 650 nm. By further employing NiOOH/FeOOH as the oxygen evolution reaction cocatalyst, the ZrS3/ZrOS/NiOOH/FeOOH photoanode yields a photocurrent density of ~9.3 mA cm-2 at 1.23 V versus the reversible hydrogen electrode with an applied bias photon-to-current efficiency of ~3.2% under simulated sunlight irradiation in an alkaline solution (pH = 13.6). The conformal ZrOS layer enables ZrS3/ZrOS/NiOOH/FeOOH photoanode operation over 1000 hours in an alkaline solution without obvious performance degradation. This study, offering a promising approach to fabricate efficient and durable photoelectrodes with earth-abundant materials, advances the frontiers of photoelectrochemical water splitting.

In situ constructing p-n heterojunction NiCo-MOF/LDH with built-in electric field for wide response range of glucose sensing

The development of non-precious metal nanomaterial for glucose sensor with sensitive performance and broad detection range will be a great challenge. In this study, a p-n heterojunction catalyst (NiCo-MOF/LDH) is devised as an efficient electrocatalytic oxidation material for glucose detection in alkaline solutions. As an enzyme-free sensor of glucose, (NiCo-MOF/LDH) exhibits good electrochemical properties with high sensitivity of 27.76 μA mM−1 cm−2, a low detection limit of 8 µM at a signal-to-noise ratio of 3 and a wide linear range (40 μM-16 mM). The results indicate that the Mott-Schottky junction between NiCo-MOF and NiCo-LDH constructs the built-in electric field (BEF) and achieves the redistribution of surface charge. The local positive charge induced by the p-n junction allows the NiCo-MOF side to adsorb more OH−, and the local negative charge allows the NiCo-LDH side to adsorb glucose positively charged H, optimizing the adsorption reactants and key intermediates. At the same time, the sensor is successfully applied to the detection of glucose in actual sample samples. Hence, the p-n heterojunction NiCo-MOF/LDH provides a rational strategy for a non-enzymatic glucose sensing catalyst.

Quantitative Analysis of Ferrate(VI) and Its Degradation Products in Electrochemically Produced Potassium Ferrate for Waste Water Treatment

Potassium ferrate(VI) (K2FeO4) as a particularly strong oxidant represents an effective and environmentally friendly waste water treatment material. When produced by anodic oxidation in highly alkaline aqueous solution, the K2FeO4 product is separated and sealed in inert plastic bags with the retention of some liquid phase with high pH. This method proved to be excellent for long-term storage at moderately low temperature (5 °C) for industrial applications. It is still imperative to check the ferrate(VI) content of the product whenever it is to be used. Fe-57 Mössbauer spectroscopy is an excellent tool for checking the ratio of ferrate(VI) to the degradation product iron(III) in a sample. For this purpose, normally the spectral areas of the corresponding subspectra are considered; however, this approximation neglects the possible differences in the corresponding Mössbauer–Lamb factors. In this work, we have successfully determined the Mössbauer–Lamb factors for the ferrate(VI) and for the most common iron(III) degradation products observed. We have found superparamagnetic behavior and low-temperature phase transformation for another iron(III) degradation product that made the determination of the Mössbauer–Lamb factors impossible in that case. The identities of a total of three different iron(III) degradation products have been confirmed.

Alkali Activation of Metakaolin and Wollastonite: Reducing Sodium Hydroxide Use and Enhancing Gel Formation through Carbonation

Alkali activated materials (AAMs) offer significant advantages over traditional materials like Portland cement, but require the use of strong alkaline solutions, which can have negative environmental impacts. This study investigates the synthesis of AAMs using metakaolin and wollastonite, aiming to reduce environmental impact by eliminating sodium silicate and using only sodium hydroxide as an activator. The hypothesis is that wollastonite can provide the necessary silicon for the reaction, with calcium from wollastonite potentially balancing the negative charges usually countered by sodium in the alkaline solution. This study compares raw and carbonated wollastonite (AAM-W and AAM-CW) systems, with raw materials carefully characterized and binding networks analyzed using TGA, FT-IR, and XRD. The results show that while wollastonite can reduce the amount of sodium hydroxide needed, this reduction cannot exceed 50%, as higher substitution levels lead to an insufficiently alkaline environment for the reactions. The carbonation of wollastonite enhances the availability of silicon and calcium, promoting the formation of both N-A-S-H and C-A-S-H gels.

Chitosan pyrolysis in the presence of a ZnCl2/NaCl salts for carbons with electrocatalytic activity in oxygen reduction reaction in alkaline solutions.

The one-step carbonization of low cost and abundant chitosan biopolymer in the presence of salt eutectics ZnCl2/NaCl results in nitrogen-doped carbon nanostructures(8.5 wt.% total nitrogen content). NaCl yields the spacious 3D structure, which allows external oxygen to easily reach the active sites for the oxygen reductionreaction (ORR) distinguished by their high onset potential and the maximum turnover frequency of 0.132 e site⁻1s⁻1. Data show that the presence of NaCl during the synthesis exhibits the formation of pores having large specific volumes and surface(specific surface area of 1217 m2g-1), and holds advantage by their pores characteristics such as their micro-size part, which provides a platform for mass transport distribution in three-dimensional N-doped catalysts for ORR. It holds benefit over sample pre-treated with LiCl in terms of the micropores specific volume and area, seen as their percentage rate, measured in the BET. Therefore, the average concentration of the active site on the surface is larger.

Ion exchange columns. A promising technology for nitrogen and phosphorus recovery in the main line of a wastewater treatment plant

Anaerobic membrane bioreactor (AnMBR) technology has great advantages for treating urban wastewaters, but, when irrigation cannot be applied and the effluent is discharged in a sensitive zone, a post-treatment of this effluent is needed for nitrogen and phosphorus removal. Under this scenario, ion exchange processes represent one of the most promising technologies for treating this effluent. Ion exchange technology allows to meet discharge limits and to recover these nutrients in a highly concentrated stream. In this work, the technical feasibility of using a commercial resin for phosphorus recovery and a natural zeolite (clinoptilolite) for nitrogen recovery was evaluated. Purolite FerrIX A33E resin removed phosphate from the AnMBR permeate within 500 Bed Volumes (BVs) with a maximum adsorption capacity (qmax) of 2,1 mg P-PO4/g resin. Regeneration of the resin (2% NaOH 2% NaCl) recovered over 95% of the phosphorous retained, achieving a concentration of 316,7 mg P-PO4/L in the regeneration solution. In the absence of a long-term study, the resin showed a stable adsorption capacity during 16 cycles of saturation-regeneration. Clinoptilolite removed nitrogen within 139 BVs obtaining a qmax of 3,68 mg N-NH4/g zeolite. 97 % of the retained N-NH4 was recovered in the regeneration stage (0,8% NaOH) with an average concentration of 577 mg N-NH4/L. Continuous exposure of the zeolite to alkaline solutions led to reduction of 50% of the adsorption capacity after 17 cycles.

Closed-Loop and Precipitation-Free CO2 Capture Process Enabled by Electrochemical pH Gradient.

Carbon dioxide (CO2) capture is a crucial negative-emission technology for the mitigation of climate change and global warming. The urgent need of combating climate change motivates the research and development of economical, effective and environmentally benign processes for CO2 capture. Herein, we design and report a flow cell for the CO2 capture from air or flue gas in a precipitate-free and closed-loop manner. No ion-exchange membrane is used in the electrolyser. The water electrolysis produces acidic solution near the anode and alkaline solution near the cathode, while generating valuable hydrogen and oxygen byproducts. The dilute CO2 in air or flue gas is captured by the alkaline solution, which is then mixed with the acidic solution to release the concentrated CO2. The process operates in a cyclic manner as driven by the water electrolysis and the mechanical pumping. No precipitation of calcium carbonate is involved for fixing CO2, which may simplify the separation process and minimizing the materials loss. The simple process enabled by electrochemical pH gradient shows promise for efficient CO2 capture on both small and large scales.

A Modified Bleaching Method for Multiplex Immunofluorescence Staining of FFPE Tissue Sections.

Multiplex immunofluorescence (mIF) staining plays an important role in profiling biomarkers and allows investigation of co-relationships between multiple biomarkers in the same tissue section. The Cell DIVE mIF platform (Leica Microsystems) employs an alkaline solution of hydrogen peroxide as a fluorophore inactivation reagent in the sequential staining, imaging, and bleaching protocol for use on FFPE sections. Suboptimal bleaching efficiency, degradation of tissue structure, and loss of antigen immunogenicity occasionally are encountered with the standard bleaching process. To overcome these impediments, we adopted a modified photochemical bleaching method, which utilizes an intense LED light exposure concurrent with the application of hydrogen peroxide. Repeated stain/bleach rounds with different antibodies were performed on breast tissue and other tissue sections. Residual signal after conventional bleaching and the modified technique were compared and tissue integrity and antigen immunogenicity were assessed. The modified technique effectively eliminates fluorescence signal from previous staining rounds and produces consistent results for multiple rounds of staining and imaging. With the modified method, photochemical treatments did not destroy tissue sub-cellular contents, and the tissue antigenicity was well preserved during the entire mIF process. Overall processing time was reduced from 36 to 30 hours in an mIF procedure with 8 rounds. With the conventional method, tissue quality was highly degraded after 8 rounds. The new technique allows reduced turn-around time, provides reliable fluorophore removal in mIF with excellent maintenance of tissue integrity, facilitating studies of the co-localization of multiple biomarkers in tissues of interest.

Self-Standing Mo/MoO2 Porous Flake Arrays for Efficient Hydrogen Evolution Reaction in High-pH Media.

The alkaline hydrogen evolution reaction (HER) is limited by scarce proton availability, resulting in slower reaction kinetics compared to those under acidic conditions. Enhancing the local chemical environment of protons on the catalyst surface can improve the intrinsic reaction kinetics. Here, we design a Mo/MoO2 metallic heterojunction that creates an acidic-like environment with a proton-rich surface, significantly enhancing HER performance in alkaline electrolytes, as confirmed by in situ spectroscopy and electrochemical analysis. A self-standing Mo/MoO2 catalytic electrode is fabricated via a controlled pyrolysis-reduction strategy. This electrode exhibits exceptional HER activity, with low overpotentials of 65 mV at 10 mA cm-2 and 315 mV at 500 mA cm-2, a Tafel slope of 38.2 mV dec-1, and stability exceeding 60 h at -300 mA cm-2 in alkaline solution. The porous flake array structure of the Mo/MoO2 heterojunctions enhances the adjacent hydronium (H3O+) concentration, resulting in a ΔGH* value of 0.15 eV and a water dissociation energy barrier of 0.37 eV in an alkaline medium. The successful preparation of a large-area electrode (2 cm × 2 cm) demonstrates the scalability of this approach for fabricating molybdenum-based catalytic electrodes with enhanced HER activity in alkaline environments.

Alkali activated materials from Tajogaite volcanic ash (La Palma, Spain): a green recovery after the 2021 eruption

The 2021 Tajogaite eruption was marked by intense pyroclastic fallout that covered a substantial portion of La Palma island, with maximum thicknesses in the central-western part. This, combined with lava flows, resulted in widespread damage to public and private properties. In this study, we investigated if volcanic ash from this eruption could serve as a raw material in the synthesis of alkali activated materials (AAMs) and contribute to the construction of eco-friendly buildings and the restoration of those damaged by the eruption. Volcanic ash-based AAMs were synthesized using NaOH and Na2SiO3 as alkaline solutions and by adding metakaolin to enhance ash reactivity and enable processing at ambient temperatures. Lightweight porous AAMs were also produced using H2O2 and metallic aluminum as foaming agents. Chemical, textural, physical, and mechanical analyses on the final products assessed their suitability as environmentally friendly materials to be used in the reconstruction of the island infrastructure, opening new perspectives on recovery actions that can be undertaken after disastrous eruptions. Of all the islands in the Canary Archipelago, La Palma has experienced the highest number of eruptions (8) in historical times, all of which showing considerable similarity in terms of eruptive mechanisms and composition to the most recent Tajogaite event. Although this study investigated fresh Tajogaite ash, similar perspectives can be envisaged for both other recent eruptions at La Palma and other similar volcanic scenarios worldwide.

Nanohybrids of B- and N-codoped reduced graphene oxide/CeO2–Co3O4 nanocomposite for efficient water oxidation

Transition metal oxides are well known as highly active and durable catalysts for the oxygen evolution reaction (OER). In this work, to enhance the electrocatalytic activity of CeO2 nanostructure in the water oxidation reaction, CeO2/Co3O4 and boron-nitrogen co-doped reduced graphene oxide incorporated (B,N-rGO) into CeO2/Co3O4 with a weight ratio of 3:1 of nanoparticles to graphene oxide were synthesized using co-precipitation and hydrothermal methods, respectively. The prepared materials were studied in detail regarding their crystal structure and morphological properties. The as-prepared materials were used as modified carbon paste electrodes for electrochemical water oxidation in an alkaline solution. The results showed that incorporating graphene oxide network into the nanoparticles structure enhances their OER performance. The material based on CeO2/Co3O4@B,N-rGO hybrid nanocomposite showed excellent OER activity with an overpotential of 410@10 mA cm−2, which is 240 and 140 mV less than that of the single CeO2 and CeO2/Co3O4 samples. Also, CeO2/Co3O4@B,N-rGO displayed the lowest Tafel slope and charge transfer resistance among the other catalysts. Moreover, the proposed catalyst displayed high stability and durability during OER. The enhanced OER performance of the CeO2/Co3O4@B,N-rGO is attributed to several catalytically active sites created by B and N doped rGO in the nanocomposite structure. The high performance of this catalyst results from the synergy of combining CeO2/Co3O4 nanoparticles with a three-dimensional co-doped rGO network.

Pt–Ni–Co trimetallic nanoparticles anchored on graphene oxide: An effective catalyst for ammonia-borane hydrolysis and direct electrooxidation of ammonia-borane in alkaline solution

In this study, graphene oxide supported platin, nickel and cobalt trimetallic nanoparticles (PtNiCo@GO) were prepared by the impregnation/reduction method. The catalytic performances of PtNiCo@GO catalysts prepared with different atomic ratios were investigated for hydrogen production and electro-oxidation of ammonia-borane (AB). For hydrolysis of ammonia-borane, Pt0.8Ni0.1Co0.1@GO catalyst exhibited higher catalytic activity than Pt0.6Ni0.2Co0.2@GO, Pt0.4Ni0.3Co0.3@GO, and Pt0.2Ni0.4Co0.4@GO. The hydrogen generation rate and turnover frequency values were found to be 540 mL min−1g−1 and 42.8 min−1, respectively, in the experiment conducted at 35 °C, 0.5 mmol AB, and 50 mg Pt0.8Ni0.1Co0.1@GO catalyst. The activation parameters (Ea, ΔH#, and ΔS#) in the catalytic hydrolysis of AB were obtained at 42.22 kJ/mol, 31.95 kJ/mol and −114.82 J/(mol × K), respectively. The effects of the PtNiCo@GO catalyst on AB electro-oxidation were made at a scanning rate of 100 mV/s in the potential range of - 1V/+1V against Ag/AgCl, and chronoamperometry measurements were made at constant potentials of - 0.2V, 0.1V and 0.4V. For cyclic voltammetry and chronoamperometry measurements, 5 mM [Fe(CN)6]3/4 (1 M KCl) redox probe and 1 M NaOH + 50 mM AB solution were used.