•Acidiplasma sp. showed robust Fe3+ regeneration during PCB thiourea leaching.•TU:Fe3+ ratio was critical to determine the Eh level and resultant Au dissolution.•The greatest Au dissolution was ...achieved via microbial Fe3+ regeneration and Eh control.•Thiourea bioleaching allowed reduction of reagents consumption.•The effectiveness of the novel thiourea bioleaching was demonstrated for the first time.
Recycling and reuse of electronic wastes (e-wastes) are becoming an increasingly critical strategy for securing metal resources as well as for minimizing environmental impacts. Thiourea leaching of gold (Au) from e-wastes can be considered an alternative to highly toxic cyanidation, provided that its reagents consumption can be largely reduced. While awareness of the use of biohydrometallurgical techniques in metal mining industries is increasing, the knowledge on microbiological precious metal solubilization is still limited. This led us to investigate and clarify for the first time the potential utility of microbiologically-mediated thiourea leaching (TU-bioleaching) of Au, with a special focus on reducing the reagents consumption while facilitating Au dissolution. Initial screening tests found that different Fe-oxidizing bacteria/archaea possessed varying degrees of thiourea tolerance (5–100 mM). When thiourea and PCB (Printed Circuit Boards) co-exist, Acidiplasma sp. Fv-Ap displayed the most robust Fe-oxidation. The Eh level during the reaction was first optimized by fluctuating the initial ratio of thiourea to Fe3+ (TU:Fe3+ = 2:1–40:1, by using 1 mM Fe3+ vs. 2–40 mM thiourea). The ratio precisely determined the Eh level during the TU-bioleaching and dictated the fate of thiourea decomposition and the resultant Au dissolution from PCB. Microbial contribution to Fe3+ regeneration was seen to support steady and continuous Au dissolution, enabling 98% Au dissolution while using low reagent concentrations of 1 mM Fe3+ and 10 mM thiourea under the microbial Eh control at around 490–545 mV. This novel TU-bioleaching process offers a new alternative approach for Au recycling from e-wastes and minimization of environmental hazards.
Ag nanoparticles reduced by organic components extracted from Jasmine tea leaves were decorated by a hydrothermal reaction on ZnO to fabricate AgNPs@ZnO composite, and then the composite was applied ...for photocatalytic reactions to degrade rhodamine B (RhB) and reduce hexavalent chromium (Cr(VI)). The produced composite (AgNPs@ZnO) was optically and physicochemically characterized to better understand the impact of the development of the AgNPs-ZnO heterojunction when compared to that of pure ZnO. The optimized AgNPs@ZnO reduced more than 95% of 10 mg/L Cr(VI) in 60 min and degraded more than 95% of 10 mg/L RhB in 180 min, with a rate constant around five times for Cr reduction and three times for RhB degradation faster than that of pure ZnO, due to its superior capacity to separate and transport photogenerated electron-hole pairs, as evidenced by a drop in photoluminescence intensity. Furthermore, when AgNPs were placed on the surface of ZnO in the composites, surface defects were generated on ZnO, as confirmed by the energy-resolved distribution of electron trap (ERDT) pattern for AgNPs@ZnO, indicating the formation of new electron trapping levels. This might cause a reduction of the energy band gap, resulting in the enhancement of light adsorption and reduction of charge recombination. Therefore, the present bio-induced composite of AgNPs@ZnO opens up new possibilities for photochemical purification technology in aquatic environments.
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•AgNPs can be produced using crude plant extract from Jasmine tea as green synthesis.•AgNPs avoid agglomeration of ZnO particles.•AgNPs@ZnO exhibit robust Cr(VI) reduction and RhB degradation.•ERDT results reveal the enhancement of electronic surface properties of AgNPs@ZnO.
The crude extract of cinnamon (after abbreviated as KM) was used to produce silver nanoparticles (AgKM). This was subsequently utilized for the hydrothermal production of a composite consisting of ...AgKM decorated on zinc oxide (AgKM/ZnO) as a photocatalyst for reducing hexavalent chromium (Cr(VI)). Several methods e.g., XRD, SEM, TEM, XPS, PL, and RDB-PAS were used to analyze the optical and physicochemical properties of ZnO/AgKM samples in order to better comprehend the impact of the development of the AgKM-ZnO heterojunction in comparison to pure ZnO. In 60 min, the optimized ZnO/AgKM reduced Cr(VI) by more than 98%, with a rate constant 63 times faster than that of pure ZnO. The enhancement of the separation and transportation of photogenerated electron-hole pairs, as proven by a decrease in photoluminescence intensity when compared with ZnO, was attributed to the composite’s higher Cr(VI) reduction rate. Also, the formation of a new electronic level was created when AgKM are loaded on the surface of ZnO in the composites, as shown by the energy-resolved distribution of the electron trap (ERDT) pattern resulting to enhancement of light absorption ability by narrowing the energy band gap. Thus, ZnO/AgKM composite’s photocatalytic efficacy was enhanced by its narrow energy band gap and reduced charge recombination. Therefore, the newly produced ZnO/AgKM composite can be used as a photocatalyst to purify Cr(VI)-containing wastewater.
The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas ...into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).
In today's world, the utilization of electronic devices, particularly mobile phones, has seen a remarkable surge and they are a valuable source of recovery of precious metals. The current study ...reports on the physical and chemical processing of mobile phone waste into leachate, followed by recovery of precious metals, using ionic liquid functionalized activated carbon (ACF). The recovery process was explored both in batch and column study. The presence of base metals in the final leachate was minimized by employing multi-stage chemical leaching, leading to a more efficient purification process. Moreover, adjustment of HCl concentration in the leachate leads to decreased in other metals interference during adsorption. Following the batch adsorption results, a favorable interaction between IL and metal complexes leads to a quantitative adsorption of the precious metals. In addition, ACF also gave an excellent performance in the column adsorption process with the high bed depth and low flow rate of the leachate as the influential parameter. An increase in the bed depth and a decrease in leachate flow rate proportionally increases the values of kTh (rate constant), qe (adsorption capacity), and KYN (rate constant) and positively increases the 50% breakthrough time (τ). Moreover, the final purification of the adsorbed metals was performed selectively through sequential desorption, employing Na2S2O3, NH4SCN, and HNO3 solutions. Finally, the adsorption capability of ACF shown a negligible change after five repetitive adsorption-desorption cycles. Thus, the current study presents a method to process mobile phone waste and selectively recover the precious metals from the leachate.
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•Activated carbon from palm kernel shell was functionalized with ionic liquid.•Mobile phone waste was physically and chemically process to extract precious metals.•ACF was able recover Au from a mobile phone leachate in batch and continuous system.•The separation of precious metals was done by sequential desorption.•ACF was able to maintain performance in a three adsorption-desorption cycles.
Recycling of gold-bearing “urban mine” resources, such as waste printed circuit boards (PCBs), is attracting an increasing interest. Some of the gold leaching techniques utilize acidic lixiviants and ...in order to eventually target such acidic leachates, the utility of the acidophilic Fe(III)-reducing heterotrophic bacterium, Acidocella (Ac.) aromatica PFBC was evaluated for production of Au(0) bionanoparticles (bio-AuNPs). Au(III) ions (as AuCl4−, initially 10 mg/L), were readily adsorbed onto the slightly-positively charged Ac. aromatica cell surface and transported into cytoplasm to successfully form intracellular bio-AuNPs in a simple one-step microbiological reaction. Generally, increasing the initial concentration of formate as e-donor corresponded to faster Au(III) bioreduction and a greater number of Au(0) nucleation sites with less crystal growth within 40-60 h: i.e., use of 1, 5, 10, or 20 mM formate led to production of bio-AuNPs of 48, 24, 13, or 12 nm in mean particle size with 2.3, 17, 62, and 97 particles/cell, respectively. Addition of Cu2+ as an enzymatic inhibitor significantly decreased the number of Au(0) nucleation sites but enhanced crystal growth of individual particles. As a result, the manipulation of the e-donor concentration combined with an enzyme inhibitor enabled the 3-grade size-control of bio-AuNPs (nearly within a normal distribution) at 48, 26 or 13 nm by use of 1 mM formate, 20 mM formate (+Cu2+) or 10 mM formate, respectively, from highly acidic, dilute Au(III) solutions.
Nanobiotechnology has tremendous potential to support eco-friendly systems and industrial sustainability through the production of metal nanoparticles using biological sources. For chemical methods ...are supposed highly toxic reagents, carcinogenic solvent, and environmental pollution. On the other hand, some of physical methods are require high energy consumption and expensive equipment. Moreover, both methods also resulted difficulties in controlling crystal growth and then triggered particle aggregation due to need additional steps by adding stabilizer. Metal nanoparticles are utilized in biosensing, medical, or pharmaceutical applications. Various types of marine organisms, including bacteria, fungi, vertebrates, invertebrates, and diverse algae, possess the ability to withstand environmental pressure and the capability to grow in the presence of high metal concentrations to synthesize metal nanoparticles. Furthermore, from the marine organisms are a source of active compound as reducing and stabilizing agents present in the biological extract. Concerning the biosynthesis of nanoparticles, gold (Au) and silver (Ag) nanoparticles have been most extensively investigated. Au and Ag nanoparticles have been synthesized using marine organisms with various sizes and shapes such as spherical, triangular, cubical, and polygonal. These nanoparticles are primarily applied in the medical field owing to their antibacterial, antioxidant, and anti-inflammatory properties. This review provides a comprehensive description of the biosynthesis of Au and Ag nanoparticles using marine organisms, including the method, mechanism of action, and their applications.
Synthesis of silver and gold nanoparticles using marine organisms and their applications. Display omitted
•Marine organism has a potential candidate to produce metal nanoparticles with avoidance of hazardous compounds, credible and sustainable reducing agents, as well as stabilizing of nanoparticles.•Metal nanoparticles is being used for bio-sensing, medical, cosmetic, or pharmaceutical applications.•Biosynthesis of gold (Au) or silver (Ag) nanoparticles (NPs) is simple process by mixing bioreagent with the HAuCl4 or AgNO3 solution and not require an increase in temperature and pressure.•The Ag/AuNPs biosynthesis can be triggered by several active compounds such as carbonyl groups, amines, amides, proteins, phenolics, and other reducing agents present in marine sources and its derivates.•The Au/AgNPs were synthesized by using marine organisms resulting in various sizes and shapes such as spherical, triangular, cubical, polygonal, and other.
Chalcopyrite flotation is selectively depressed by oxidation treatment. The presence of ferric oxyhydroxide on the surface of chalcopyrite after oxidation treatment is a key factor in depressing ...chalcopyrite flotation. However, there is no concrete evidence that ferric oxyhydroxide has a depressing effect. In addition, the effectiveness of this depressing effect could be enhanced by directly applying ferric oxyhydroxide nanoparticles. This study investigated the effect of goethite (α-FeOOH) nanoparticles on the surface properties and flotation behavior of chalcopyrite. α-FeOOH nanoparticles were produced through chemical precipitation followed by hydrothermal treatment. The crystalline structure of irregular rice grain-shaped α-FeOOH nanoparticles was confirmed by the X-ray diffraction pattern and scanning electron microscope image. Micro-flotation experiments showed that chalcopyrite recovery decreased significantly from 93 % to 13 % when 30 mg/L α-FeOOH nanoparticles was used. This flotation result demonstrated the potential of α-FeOOH nanoparticles as a nanodepressant for the flotation of chalcopyrite. These nanoparticles physically adsorbed on the chalcopyrite surface and rendered its surface hydrophilic, thereby reducing the chalcopyrite flotation recovery. The attractive electrostatic force between the positively charged α-FeOOH nanoparticles and the negatively charged chalcopyrite surface is likely responsible for the adsorption of α-FeOOH nanoparticles on chalcopyrite.
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The effect of goethite nanoparticles (Nps) on the flotation of chalcopyrite is studied.Goethite (α-FeOOH) Nps deplete the flotation recovery of chalcopyrite.α-FeOOH Nps alter the surface hydrophobicity of chalcopyrite.α-FeOOH Nps and chalcopyrite have opposite charges and are attracted electrostatically.
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