Metabolism of metals in microalgae and adaptation to metal excess are of significant environmental importance. We report a three-step mechanism that the green microalga Chlorella sorokiniana activates during the acquisition of and adaptation to manganese (Mn), which is both an essential trace metal and a pollutant of waters. In the early stage, Mn2+ was mainly bound to membrane phospholipids and phosphates in released mucilage. The outer cell wall was reorganized and lipids were accumulated, with a relative increase in lipid saturation. Intracellular redox settings were rapidly altered in the presence of Mn excess, with increased production of reactive oxygen species that resulted in lipid peroxidation and a decrease in the concentration of thiols. In the later stage, Mn2+ was chelated by polyphosphates and accumulated in the cells. The structure of the inner cell wall was modified and the redox milieu established a new balance. Polyphosphates serve as a transient Mn2+ storage ligand, as proposed previously. In the final stage, Mn was stored in multivalent Mn clusters that resemble the structure of the tetramanganese-calcium core of the oxygen-evolving complex. The present findings elucidate the bioinorganic chemistry and metabolism of Mn in microalgae, and may shed new light on water-splitting Mn clusters.
This paper focuses on the recent advances on radiolysis-assisted shape-controlled synthesis of noble metal nanostructures. The techniques and protocols for producing desirable shapes of noble metal nanoparticles are discussed through introducing the critical parameters which can influence the nucleation and growth mechanisms. Nucleation rate plays a vital role on the crystallinity of seeds while growth rate of different seeds' facets determines the final shape of resultant nanoparticles. Nucleation and growth rate both can be altered with factors such as absorbed dose, capping agents, and experimental environment condition to control the final shape. Remarkable physical and chemical properties of synthesized noble metal nanoparticles by controlled morphology have been systematically evaluated to fully explore their applications.
Photocatalytic remediation of industrial water pollution has courted intense attention lately due to its touted green approach. In this respect, Keggin-based polyoxometalates (POMs) as green solid acids in photocatalytic reaction possess superior qualities, viz. unique photoinduced charge-transfer properties, strong photooxidative-photoreductive ability, high chemical and thermal stability, and so forth. Unfortunately, it suffers from a large bandgap energy, low specific surface area, low recoverability, and scarce utilization in narrow absorption range. Therefore, the pollutant degradation performance is not satisfactory. Consequently, multifarious research to enhance the photocatalytic performance of Keggin-based POMs were reported, viz. via novel modifications and functionalizations through a variety of materials, inclusive of, inter alia, metal oxides, transition metals, noble metals, and others. In order to advocate this emerging technology, current review work provides a systematic overview on recent advancement, initiated from the strategized synthetic methods, followed by hierarchical enhancement and intensification process, at the same time emphasizes on the fundamental working principles of Keggin-based POM nanocomposites. By reviewing and summarizing the efforts adopted global-wide, this review is ended with providing useful outlooks for future studies. It is also anticipated to shed light on producing Keggin-based POM nanocomposites with breakthrough visible- and solar-light-driven photocatalytic performance against recalcitrant organic waste.
Waste residues and acidic effluents (post-processing of E-waste) released into the local surroundings cause perilous environmental threats and potential risks to human health. Only limited research and information are available toward the sustainable management of waste residues generated post resource recovery of E-waste components. In the present study, the manual processing of obsolete computer (keyboard, monitor, CPU, and mouse) and chemical leaching of waste printed circuit boards (WPCBs) (motherboard, hard drive, DVD drive, and power supply) were performed for urban mining. The toxicity characteristics of typical pollutants in the residues of the WPCBs (post chemical leaching) were studied by toxicity characteristics leaching procedure (TCLP) test. Manual dismantling techniques resulted in an efficient urban mining concept with an overall average profit estimation of INR 2513.73/US$ 34.59. The chemical leaching of WPCBs showed a high concentration of metal leaching like Cu (229662 ± 575.3 mg/kg) and Pb (36785.67 ± 13.07 mg/kg) in the motherboard after stripping epoxy coating. The toxicity test revealed that the concentration of Cu (245.746 ± 0.016 mg/l) in the treated waste residue and Cu (430.746 ± 0.0015 mg/l) and Pb (182.09 ± 0.0035 mg/l) in the non-treated waste residue exceeded the threshold limit. The concentrations of other elements As, Cd, Co, Cr, Ag, Mn, Zn, Ni, Fe, Se, and In were within the permissible limit. Hence, the waste residue stands non-hazardous except Cu and Pb. Stripping out the epoxy coating of WPCBs enhances the metal leaching concentrations. The study highlighted that efficient and appropriate E-waste urban mining has immense potential in tracing the waste scrap into secondary resources. This study also emphasized that the final processed waste residue (left unattended or discarded due to lack of appropriate skill and technology) can be taken into consideration and exploited for value-added materials.
There is limited information on the optimal processes to remove heavy metals in greywater. A Response Surface Methodology (RSM) via the Box-Behnken Design (BBD) approach was applied in this study to investigate and optimise the process variables of activation time (1.5-2.5 h), impregnation ratio (0.25-0.75) and zinc chloride (ZnCl2) percentage (20-60%) for the removal of heavy metal ions (Cd, Cu, Pb and Ni) associated with greywater treatment. The quadratic model was chosen to describe the effects of the process variables (activation time, impregnation ratio, ZnCl2 percentage) on predicting the responses (heavy metal ions removal) with low p-values (
Sewage sludge has long been regarded as a hazardous waste by virtue of the loaded heavy metals and pathogens. Recently, more advanced technologies are introduced to make use of the nutrients from this hazardous sludge. Successful recovery of sludge's carbon content could significantly convert waste to energy and promote energy sustainability. Meanwhile, the recovery of nitrogen and trace minerals allows the production of fertilizers. This review is elucidating the performances of modern thermal treatment technologies in recovering resources from sewage sludge while reducing its environmental impacts. Exhaustive investigations show that most modern technologies are capable of recovering sludge's carbon content for energy generation. Concurrently, the technologies could as well stabilize heavy metals, destroy harmful pathogens, and reduce the volume of sludge to minimize the environmental impacts. Nevertheless, the high initial investment cost still poses a huge hurdle for many developing countries. Since the initial investment cost is inevitable, the future works should focus on improving the profit margin of thermal technologies; so that it would be more financially attractive. This can be done through process optimization, improved process design as well as the use of suitable co-substrates, additives, and catalyst as propounded in the review.
Metal nanoclusters have been considered as a new class of chemical sensors due to their unique electronic structures and the particular physicochemical properties. The interaction of N2 molecule with neutral and ionic magnesium nanoclusters Mg17q(q=0,±1), as well as neutral magnesium nanoclusters with the centrality of beryllium and calcium Mg16M (M=Be, Mg, and Ca) have been investigated using CAM-B3LYP/6-311+G(d) level of theory in the gas phase. The electronic properties of magnesium nanoclusters were significantly affected by the adsorption of N2 molecule. The NBO analysis revealed a charge transfer from the adsorbed N2 molecule to the nanocluster. Based on the adsorption energies and enthalpies, a thermodynamically favorable chemisorption process was predicted for the Mg16Ca-N2 complex. The negative value of the Gibbs free energy of Mg16Ca-N2 confirmed the spontaneous adsorption process. The estimated recovery time for Mg16Ca-N2 complex for 8-MR (0.089 s) and 4-MRs (0.075 s) illustrated a possible desorption process for N2 molecule from the surface of Mg16Ca. Our finding also revealed the Mg16Ca has the ability to use as a sensor for detection and absorption of N2 molecule.
There is a global need to use plants to restore the ecological environment. There is no systematic review of phytoremediation mechanisms and the parameters for environmental pollution. Here, we review this situation and describe the purification rate of different plants for different pollutants, as well as methods to improve the purification rate of plants. This is needed to promote the use of plants to restore the ecosystems and the environment. We found that plants mainly use their own metabolism including the interaction with microorganisms to repair their ecological environment. In the process of remediation, the purification factors of plants are affected by many conditions such as light intensity, stomatal conductance, temperature and microbial species. In addition the efficiency of phytoremediation is depending on the plants species-specific metabolism including air absorption and photosynthesis, diversity of soil microorganisms and heavy metal uptake. Although the use of nanomaterials and compost promote the restoration of plants to the environment, a high dose may have negative impacts on the plants. In order to improve the practicability of the phytoremediation on environmental restoration, further research is needed to study the effects of different kinds of catalysts on the efficiency of phytoremediation. Thus, the present review provides a recent update for development and applications of phytoremediation in different environments including air, water, and soil.
The discharge of high levels of heavy metals into the environment is of concern due to its toxicity to aquatic life and potential human health impacts. Biofiltration systems have been used in urban environments to address nutrient contamination, but there is also evidence that such systems can be effective in reducing heavy metals concentration in stormwater. However, the accumulation pattern of heavy metals and lifespan of such systems, which are important in engineering design, have not been thoroughly explored. This study investigated the accumulation patterns of lead (Pb), copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe), which are common in urban runoff, in non-vegetated filtration columns using three different types of filter media, namely sand (S), and mixtures of sand with fly ash (sand-fly ash mix, SF), and with zeolite (sand-zeolite mix, SZ). The columns were assessed in terms of infiltration rate, the mass of heavy metals accumulation at different depths, and formation of crust layer (schmutzdecke) at the surface. The results show that most of the heavy metals accumulated at the top 5-10 cm of the filter media. However, Zn was found adsorbed to a depth of 15 cm in S and SZ columns, while Mn and Fe were present in column S throughout the entire 30 cm depth of the filter media. The presence especially of Zn, Mn, and Fe in the deeper portions of the filter media before the top 5 cm layer reached its maximum adsorption capacity, hints that transport to the deeper layers is not necessarily dependent on saturation of the upper layers for these heavy metals. SF accumulated heavy metals most at the top 5 cm of the filter media layer, and retained twice the mass of heavy metals in the crust layer, compared to S and SZ columns. SF also yielded the lowest value of infiltration rate of 31 mm/h. Considering both metals accumulation and clogging potential of the filter media, the periodic maintenance of these systems is suggested to be approximately between 1.5 and 3 years.
Nanowires have been utilized widely in the generation of high-performance nanosensors. Laser ablation, chemical vapor, thermal evaporation and alternating current electrodeposition are in use in developing nanowires. Nanowires are in a great attention because of their submicron feature and their potentials in the front of nanoelectronics, accelerated field effect transistors, chemical- and bio-sensors, and low power consuming light-emitting devices. With the control of nanowire size and concentration of dopant, the electrical sensitivity and other properties of nanowires can be tuned for the reproducibility. Nanowires comprise of arrays of electrodes that form a nanometer electrical circuit. One of advantages of nanowires is that they can be fabricated in nanometer-size for various applications in different approaches. Several studies have been conducted on nanowires and researchers discovered that nanowires have the potential in the applications with material properties at the nanometer scale. The unique electrical properties of nanowires have made them to be promising for numerous applications. Nowadays, for example, MOS field-effect transistors are largely used as fundamental building elements in electronic circuits. Also, the dimension of MOS transistors is gradually decreasing to the nanoscale based on the prediction made by Moor's law. However, their fabrication is challenging. This review summarized different techniques in the fabrication of nanowires, global nanowire prospect, testing of nanowires to understand the real electrical behavior using higher resolution microscopes, and brief applications in the detection of biomolecules, disease such as corona viral pandemic, heavy metal in water, and applications of nanowires in agriculture.
A practical and facile synthesis of various coumarin derivatives was conducted using a liquid phase of 4,4'-trimethylenedipiperidine as a safe and greener dual-task reagent under catalyst-free and solvent-free conditions. This reagent is a commercially available solid and can be handled easily, having a liquid phase over a vast temperature range, high thermal stability, low toxicity, and good solubility in green solvents such as water and ethanol. It is worth mentioning that 4,4'-trimethylenedipiperidine could be completely recovered and regenerated after a simple process. The current method has other merits, including (a) minimizing the use of high-risk and toxic reagents and solvents; (b) the use of a secure and recoverable medium-organocatalyst instead of metal-based catalysts, (c) avoid tedious processes, harsh conditions, and a multi-step process for the preparation of catalysts, (d) transform phenol and salicyladehyde derivatives into the corresponding coumarin derivatives in good to high yields, (e) minimize hazardous waste generation. TMDP could be easily recovered and reused several times with no change in its activity. Furthermore, the current work demonstrated that the liquid phase of 4,4'-trimethylenedipiperidine can be a promising medium in organic reaction at higher temperatures due to its broad liquid range temperature, thermal stability, acceptor/donor hydrogen bond property, and other unique merits. New methodology for the synthesis of coumarines using liquid phase of TMDP under mild conditions.
The emergence and continual accumulation of industrial micropollutants such as dyes, heavy metals, organic matters, and pharmaceutical active compounds (PhACs) in the ecosystem pose an alarming hazard to human health and the general wellbeing of global flora and fauna. To offer eco-friendly solutions, living and non-living algae have lately been identified and broadly practiced as promising agents in the bioremediation of micropollutants. The approach is promoted by recent findings seeing better removal performance, higher efficiency, surface area, and binding affinity of algae in various remediation events compared to bacteria and fungi. To give a proper and significant insight into this technology, this paper comprehensively reviews its current applications, removal mechanisms, comparative efficacies, as well as future outlooks and recommendations. In conducting the review, the secondary data of micropollutants removal have been gathered from numerous sources, from which their removal performances are analyzed and presented in terms of strengths, weaknesses, opportunities, and threats (SWOT), to specifically examine their suitability for selected micropollutants remediation. Based on kinetic, isotherm, thermodynamic, and SWOT analysis, non-living algae are generally more suitable for dyes and heavy metals removal, meanwhile living algae are appropriate for removal of organic matters and PhACs. Moreover, parametric effects on micropollutants removal are evaluated, highlighting that pH is critical for biodegradation activity. For selective pollutants, living and non-living algae show recommendable prospects as agents for the efficient cleaning of industrial wastewaters while awaiting further supporting discoveries in encouraging technology assurance and extensive applications.
Water bodies are being polluted rapidly by disposal of toxic chemicals with their huge entrance into drinking water supply chain. Among these pollutants, heavy metal ions (HMIs) are the most challenging one due to their non-biodegradability, toxicity, and ability to biologically hoard in ecological systems, thus posing a foremost danger to human health. This can be addressed by robust, sensitive, selective, and reliable sensing of metal ions which can be achieved by Metal organic frameworks (MOF) based electrochemical sensors. In the present era, MOFs have caught greater interest in a variety of applications including sensing of hazardous pollutants such as heavy metal ions. So, in this review article, types, synthesis and working mechanism of MOF based sensors is explained to give general overview with updated literature. First time, detailed study is done for sensing of metal ions such as chromium, mercury, zinc, copper, manganese, palladium, lead, iron, cadmium and lanthanide by MOFs based electrochemical sensors. The use of MOFs as electrochemical sensors has attractive success story along with some challenges of the area. Considering these challenges, we attempted to highlight the milestone achieved and shortcomings along with future prospective of the MOFs for employing it in electrochemical sensing devices for HMIs. Finally, challenges and future prospects have been discussed to promote the development of MOFs-based sensors in future.
Land exploitation for mining sector may leave a series of environmental impacts on our ecosystem if not appropriately managed. Therefore, the present study attempts to evaluate the various environmental aspects due to abandoned metal mining including former iron ore, bauxite, and tin mining lands in view of its hydrogeochemical behavior. Mine-impacted waters and sediments were ascertained from former mining ponds, mine tailings, and impacted streams for interpretation of aqueous and sediment geochemistry, major and trace elements, hydrochemical facies, chemical weathering rate and CO2 consumption, and water quality classification. Results indicated that the environmental impact of the long-abandoned iron ore mine was still evident with some high concentration of metals and acidic pH. Higher concentrations of Fe and Mn in water were noticeable in some areas while other trace elements (Pb, Zn, As, Cd, Cr, and Cu) were found below the recommended guideline values. Sediment quality reflected the trend of water quality variables mainly associated with metal(loid) elements, resulting in potential ecological risk, classified as having low to moderate risk. There were variations in terms of hydrochemical facies of the waters suggesting the influence of minerals in water. The chemical weathering rate suggests that contribution of carbonate mineral weathering was more important (up to 60%) than silicate weathering. The resulting CO2 consumption by mineral weathering was estimated to be in the range of 1.7-9.8 × 107 mol/year (former bauxite and tin mining areas can act as temporary sinks for CO2). Water quality classifications according to several chemical indices (Kelly's ratio, sodium absorption ratio, soluble sodium percentage, residual sodium carbonate, magnesium absorption ratio, and permeability index) were also discussed in regards to mine water reuse for irrigation purpose. The findings suggest that a holistic approach that integrates all important hydrogeochemical aspects is essential for a thorough evaluation of the implication of medium- to long-term mining exploitation on its surrounding ecosystems. This would be beneficial in light of restoration potential of degraded mining land so as for future mitigation strategies in the mining sector.
Phytoremediation is a biological remediation technique known for low-cost technology and environmentally friendly approach, which employs plants to extract, stabilise, and transform various compounds, such as potentially toxic elements (PTEs), in the soil or water. Recent developments in utilising chelating agents soil remediation have led to a renewed interest in chelate-induced phytoremediation. This review article summarises the roles of various chelating agents and the mechanisms of chelate-induced phytoremediation. This paper also discusses the recent findings on the impacts of chelating agents on PTEs uptake and plant growth and development in phytoremediation. It was found that the chelating agents have increased the rate of metal absorption and translocation up to 45% from roots to the aboveground plant parts during PTEs phytoremediation. Besides, it was also explored that the plants may experience some phytotoxicity after adding chelating agents to the soil. However, due to the leaching potential of synthetic chelating agents, the use of organic chelants have been explored to be used in PTEs phytoremediation. Finally, this paper also presents comprehensive insights on the significance of using chelating agents through SWOT analysis to discuss the advantages and limitations of chelate-induced phytoremediation.
In this study, concentrations of Cd, Ni, Pb, and Cr were determined in tobacco, tobacco smoke-condensate, and cigarette ash for selected brands used in Pakistan. Smoking apparatus was designed for metal extraction from cigarette smoke. Samples were digested through microwave digester and then analyzed by flame atomic absorption spectrophotometer (FAAS). Higher concentration of Ni was detected in imported brands than the counterparts in the local brands. Pb levels were however higher in local brands while significant concentration of Cd was observed in both brands. For Cr, the level in tobacco of local brands was higher than their emitted smoke, whereas imported brands showed higher level in smoke than in tobacco. The cigarette ash retained 65 to 75% of the metal and about 25 to 30% went into the body. While this study revealed the serious requirement to standardize the manufacturing of tobacco products, more importantly is the urgent need for stronger enforcements to put in place to alert the general population about the hazardous effects of cigarettes and the health risks associated with these toxic metals.
The sequential extraction procedure proposed by the European Standard, Measurements and Testing (SM&T) program, formerly the Community Bureau of Reference (BCR), was applied for partitioning of heavy metals (HMs) in river sediments collected along the course of Sungai Buloh and the Straits of Malacca in Selangor, Malaysia. Eight elements (V, Pb, Cd, Cr, Co, Ni, Cu and Zn) from seven stations (S1-S7) and at different depths were analyzed using the modified BCR Sequential Extraction Procedure (SEP) in combination with ICP-MS to obtain the metal distribution patterns in this region. The results showed that heavy metal contaminations at S2 and S3 was more severe than at other sampling sites, especially for Zn, Cu, Ni and Pb. Nevertheless, the element concentrations from top to bottom layers decreased predominantly. The samples from the Straits of Malacca (S4-S7) the highest contamination factors obtained were for Co, Zn and Pb while the lowest were found for V and Cr, similar to Sungai Buloh sediments. The sediments showed a low risk for V, Cr, Cu and Pb with RAC values of less than 10%, but medium risk for Co, Zn (except S3), Cd at S1 and S2 and Ni at S1, S3 and S5. Zn at S3 and Cd at S3-S7 showed high risk to our sediment samples. There is not any element of very high risk conditions in the selected samples.
Herein, two stable lead(II) molecular-bowl-based metal-organic frameworks and their micro- and nanosized forms with open metal sites were presented. These materials could act as Lewis acid catalysts to cyanosilylation reaction. Moreover, the catalytic performances are size-dependent, with the catalyst with nanosized form being 1 order of magnitude more efficient than those with micro- and millisized forms.
In this study, performances of mesoporous Mo/Al2O3 catalysts prepared by sol-gel and post-hydrolysis methods in hydrocracking of atmospheric residual oil were compared. In addition, different methods: (i) the single step and (ii) conventional impregnation method to incorporate active metal over the mesoporous support were also investigated. For single step method, Mo/Al2O3 catalysts were synthesized directly by sol-gel and post-hydrolysis method. On the other hand, the impregnation method was a two step procedure which involved the production of alumina via sol-gel or post-hydrolysis method and followed by respective Mo impregnation. In general, mesoporous Mo/Al2O3 catalysts prepared by sol-gel method resulted in relatively higher surface area (> 400 m2/g) and large pore volume (- 0.8 cm3/g). Mo/Al2O3 catalysts prepared by sol-gel method exhibited higher hydrocracking activity as well. The Mo crystal size was found to relate directly with the hydrocracking result.