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.
Metal Organic Frameworks (MOFs) represent a promising class of metallic catalysts for reduction of nitrogen-containing contaminants (NCCs), such as 4-nitrophenol (4-NP). Nevertheless, most researches involving MOFs for 4-NP reduction employ noble metals in the form of fine powders, making these powdered noble metal-based MOFs impractical and inconvenient for realistic applications. Thus, it would be critical to develop non-noble-metal MOFs which can be incorporated into macroscale and porous supports for convenient applications. Herein, the present study proposes to develop a composite material which combines advantageous features of macroscale/porous supports, and nanoscale functionality of MOFs. In particular, copper foam (CF) is selected as a macroscale porous medium, which is covered by nanoflower-structured CoO to increase surfaces for growing a cobaltic MOF, ZIF-67. The resultant composite comprises of CF covered by CoO nanoflowers decorated with ZIF-67 to form a hierarchical 3D-structured catalyst, enabling this ZIF-67@Cu foam (ZIF@CF) a promising catalyst for reducing 4-NP, and other NCCs. Thus, ZIF@CF can readily reduce 4-NP to 4-AP with a significantly lower Ea of 20 kJ/mol than reported values. ZIF@CF could be reused over 10 cycles and remain highly effective for 4-NP reduction. ZIF@CF also efficiently reduces other NCCs, such as 2-nitrophenol, 3-nitrophenol, methylene blue, and methyl orange. ZIF@CF can be adopted as catalytic filters to enable filtration-type reduction of NCCs by passing NCC solutions through ZIF@CF to promptly and conveniently reduce NCCs. The versatile and advantageous catalytic activity of ZIF@CF validates that ZIF@CF is a promising and practical heterogeneous catalyst for reductive treatments of NCCs.
Phytoremediation is considered as a cost-effective and environmentally friendly
technique for decontaminating environments that have been contaminated with
heavy metal ions. The technique describes the use of plants and their concomitant
microbes to mitigate environmental contaminations. However, conventional
remediation techniques like chemical, thermal and physical treatment methods are
too costly, and may end of causing more contamination to the environment.
Phytoremediation practice provides a major information on the utilization of plants
and their materials in decontaminating polluted environments. Heavy metals and
other organic contaminants are among the most precarious substances released into
the environment which have an eminent level of toxicity and sturdiness of both
aquatic and terrestrial organisms. The review aimed at providing a broad
understanding of utilizing various plants and their materials in decontaminating
polluted environments with heavy metals and other organic contaminants. It also
provided the general methods used in treating the aforementioned contaminants in
an environment. The review further discussed the classes of phytoremediation like
phytoextraction, phytovolatilisation, phytostabilization, phytotransformation,
phytodegradation and phytofiltration. The generalized advantages and disadvantages
of phytoremediation were ultimately highlighted.
Increasing toxic metal content in aquatic products has become a universal burden due to the risks to aquatic organisms and human health associated with the consumption of these products. In this study, toxic metal distribution and accumulation in the organs of fish and bivalve species of economic and culinary importance from the lower reaches of the Yangtze River are examined, and the corresponding health risks are also investigated. In general, the viscera and gill show higher concentration of metals than other tissues. The order of the accumulation sequence of metals in muscle tissue of fish and bivalve is Zn > Cu > Mn > Cr > As > Hg > Pb > Cd and Mn > Zn > Cu > As > Cr > Pb > Cd > Hg respectively. Maximum accumulation of Mn (507.50 μg g-1) and Pb (0.51 μg g-1) in the gill tissues indicates the major uptake of these metals from the water column. According to the Hazard Index (HI) calculations (based on USEPA), the analyzed metals will not cause any harmful health effects to individuals for both normal and habitual fish consumers, except for Hg and As in habitual consumers, if these species are consumed at a larger amount. Compared to the Chinese Food Health Criterion and other international standards (WHO/FAO), metal concentrations in the edible muscle tissues of the studied species are lesser than the acceptable levels and found to be fit for human consumption.
The microbial breakdown of chitosan, a fishery waste-based material, and its derivative cross-linked chitosans, in both non-contaminated and contaminated conditions was investigated in a laboratory incubation study. Biodegradation of chitosan and cross-linked chitosans was affected by the presence of heavy metals. Zn was more pronounced in inhibiting microbial activity than Cu and Pb. It was estimated that a longer period is required to complete the breakdown of the cross-linked chitosans (up to approximately 100 years) than unmodified chitosan (up to approximately 10 years). The influence of biodegradation on the bioavailable fraction of heavy metals was studied concurrently with the biodegradation trial. It was found that the binding behaviour of chitosan for heavy metals was not affected by the biodegradation process.
In this study, the particle size distribution and concentration of metallic elements of solvent- and water-based paint dust from bulk dust collected from dust-collecting hoppers were determined. The mean particle size diameter over a 12-week sampling period was determined using a particle size analyzer. The metals composition and concentration of the dust were determined via acid digestion technique followed by concentration analysis using inductively coupled plasma. The volume weighted mean particle diameters were found to be 0.941+/-0.016 and 8.185+/-0.201 microm for solvent- and water-based paint dust, respectively. The mean concentrations of metals in solvent-based paint dust were found to be 100+/-20.00 microg/g (arsenic), 1550+/-550.00 microg/g (copper), 15,680+/-11,780.00 microg/g (lead) and 30,460+/-10,580.00 microg/g (zinc) while the mean concentrations of metals in water-based paint dust were found to be 20.65+/-6.11 microg/g (arsenic), 9.14+/-14.65 microg/g (copper), 57.46+/-22.42 microg/g (lead) and 1660+/-1260 microg/g (zinc). Both paint dust types could be considered as hazardous since almost all of the dust particles were smaller than 10 microm. Particular emphasis on containment of solvent-based paint dust particles should be given since it was shown that they were very fine in size (<1 microm) and had high lead and zinc concentrations.
This study focuses on the fabrication and electrical characterization of a polymer composite based on nano-sized varistor powder. The polymer composite was fabricated by the melt-blending method. The developed nano-composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FeSEM), and energy-dispersive X-ray spectroscopy (EDAX). The XRD pattern revealed the crystallinity of the composite. The XRD study also showed the presence of secondary phases due to the substitution of zinc by other cations, such as bismuth and manganese. The TEM picture of the sample revealed the distribution of the spherical, nano-sized, filler particles throughout the matrix, which were in the 10-50 nm range with an average of approximately 11 nm. The presence of a bismuth-rich phase and a ZnO matrix phase in the ZnO-based varistor powder was confirmed by FeSEM images and EDX spectra. From the current-voltage curves, the non-linear coefficient of the varistor polymer composite with 70 wt% of nano filler was 3.57, and its electrical resistivity after the onset point was 861 KΩ. The non-linear coefficient was 1.11 in the sample with 100 wt% polymer content. Thus, it was concluded that the composites established a better electrical non-linearity at higher filler amounts due to the nano-metric structure and closer particle linkages.
Hybrid artificial intelligence (AI) models are developed for sediment lead (Pb) prediction in two Bays (i.e., Bramble (BB) and Deception (DB)) stations, Australia. A feature selection (FS) algorithm called extreme gradient boosting (XGBoost) is proposed to abstract the correlated input parameters for the Pb prediction and validated against principal component of analysis (PCA), recursive feature elimination (RFE), and the genetic algorithm (GA). XGBoost model is applied using a grid search strategy (Grid-XGBoost) for predicting Pb and validated against the commonly used AI models, artificial neural network (ANN) and support vector machine (SVM). The input parameter selection approaches redimensioned the 21 parameters into 9-5 parameters without losing their learned information over the models' training phase. At the BB station, the mean absolute percentage error (MAPE) values (0.06, 0.32, 0.34, and 0.33) were achieved for the XGBoost-SVM, XGBoost-ANN, XGBoost-Grid-XGBoost, and Grid-XGBoost models, respectively. At the DB station, the lowest MAPE values, 0.25 and 0.24, were attained for the XGBoost-Grid-XGBoost and Grid-XGBoost models, respectively. Overall, the proposed hybrid AI models provided a reliable and robust computer aid technology for sediment Pb prediction that contribute to the best knowledge of environmental pollution monitoring and assessment.
Structural parameters, electronic structure and optical properties of the dialkali metal monotelluride M2Te (M = Li, Na, K and Rb) compounds in the cubic antifluorite structure were investigated via ab initio calculations using the all electron linearized augmented plane wave approach based on density functional theory with and without including spin-orbit coupling (SOC). The exchange-correlation interactions were described within the PBEsol version of the generalized gradient approximation and Tran-Blaha modified Becke-Johnson potential (TB-mBJ). Optimized equilibrium lattice parameters are in excellent accordance with existing measured ones. Computed energy band dispersions show that the studied compounds are large band gap materials. Inclusion of SOC reduces the band gap value compared to the corresponding one calculated without including SOC. Determination of the energy band character and interatomic bonding nature are performed using the densities of states diagrams and charge density distribution map. Linear optical function spectra are predicted for a wide energy range and the origin of the dielectric function spectrum peaks are determined.
The dispersion of hyperaccumulators used in the phytoremediation process has caused environmental concerns because of their heavy metal (HM) richness. It is important to reduce the environmental risks and prevent the HM to reenter the ecological cycle and thereby the human food web. In this work, supercritical water gasification (SCWG) technology was used to convert Sedum plumbizincicola into hydrogen (H2) gas and to immobilize HMs into biochar. The H2 production correlated with temperature ranging from 380 to 440 ℃ with the highest H2 yield of 2.74 mol/kg at 440 ℃. The free-radical reaction and steam reforming reaction at high temperatures were likely to be the mechanism behind the H2 production. The analyses of bio-oil by the Gas Chromatography-Mass Spectrometer (GC-MS) and Nuclear magnetic resonance spectroscopy (NMR) illustrated that the aromatic compounds, oxygenated compounds, and phenols were degraded into H2-rich gases. The increase of temperature enhanced the HM immobilization efficiency (>99.2 % immobilization), which was probably due to the quickly formed biochar that helped adsorb HMs. Then those HMs were chemically converted into stable forms through complexation with inorganic components on biochar, e.g., silicates, SiO2, and Al2O3. Consequently, the SCWG process was demonstrated as a promising approach for dispersing hyperaccumulators by immobilizing the hazardous HMs into biochar and simultaneously producing value-added H2-rich gases.
Spatial and temporal variations in concentrations of several metals and isotopes in sediment cores from around Penang Island, an area with economically important biological resources off the northwest coast of peninsular Malaysia, are reported. Because of a typical, monazite rich mineralogy in surrounding drainage basins, sedimentary metal enrichment factors relative to global average materials, enrichment factors (EFs) of ˃1.0 do not always indicate significant anthropogenic metal inputs. Because of extensive metal solubilization in the hot, organic carbon rich area, EFs of < 1.0 may be observed for several metals despite significant anthropogenic contributions. Comparison of metal-Al relationships in Penang area surface sediments with those in nearby and presumed uncontaminated Strait of Malacca sediments more accurately correct for atypical regional solubilization and mineralogical effects than comparison to global average materials. Such comparisons show concentrations of Cd, Cu, Pb, Ni, Cr, As, Sb, Zn and V have changed by less than a factor of two by anthropogenic discharges. Sedimentary concentration profiles of Pb, Zn and Cu, ratioed to Sc to normalize for variations in grain size and mineralogy, have subsurface maxima suggestive of modest and recently reduced anthropogenic inputs. Mn, U, As and Sb have Sc-normalized concentration profiles clearly affected by diagenetic processes. Sc-normalized profiles of Cr, Th, Ce and Sm show only small changes with depth, confirming insignificant anthropogenic inputs and undetectable postdepositional diagenetic mobility.
Excess ²¹⁰Pb activities and fluxes in Penang area sediments are limited by supply of this radionuclide, in contrast to sediments of both the northwestern U.S.A. and Amazon continental shelves, where they are limited by particle scavenging reactions.²¹⁰Pb activities in sediments of
the shallow, dynamic Penang area often show erratic or unconvincing changes with depth that
cannot be reliably modeled by assuming steady state, constant deposition rate of particles of
uniform chemistry, mineralogy and initial unsupported ²¹⁰Pb, and that mixing is limited to a
recognizable surface layer and resemble a diffusive process.
Graphene-based adsorbents have attracted wide interests as effective adsorbents for heavy metals removal from the environment. Due to their excellent electrical, mechanical, optical and transport properties, graphene and its derivatives such as graphene oxide (GO) have found various applications. However, in many applications, surface modification is necessary as pristine graphene/GO may be ineffective in some specific applications such as adsorption of heavy metal ions. Consequently, the modification of graphene/GO using various metals and non-metals is an ongoing research effort in the carbon-material realm. The use of organic materials represents an economical and environmentally friendly approach in modifying GO for environmental applications such as heavy metal adsorption. This review discusses the applications of organo-functionalized GO composites for the adsorption of heavy metals. The aspects reviewed include the commonly used organic materials for modifying GO, the performance of the modified composites in heavy metals adsorption, effects of operational parameters, adsorption mechanisms and kinetic, as well as the stability of the adsorbents. Despite the significant research efforts on GO modification, many aspects such as the interaction between the functional groups and the heavy metal ions, and the quantitative effect of the functional groups are yet to be fully understood. The review, therefore, offers some perspectives on the future research needs.
Biocompatible metals have been revolutionizing the biomedical field, predominantly in human implant applications, where these metals widely used as a substitute to or as function restoration of degenerated tissues or organs. Powder metallurgy techniques, in specific the metal injection moulding (MIM) process, have been employed for the fabrication of controlled porous structures used for dental and orthopaedic surgical implants. The porous metal implant allows bony tissue ingrowth on the implant surface, thereby enhancing fixation and recovery. This paper elaborates a systematic classification of various biocompatible metals from the aspect of MIM process as used in medical industries. In this study, three biocompatible metals are reviewed-stainless steels, cobalt alloys, and titanium alloys. The applications of MIM technology in biomedicine focusing primarily on the MIM process setting parameters discussed thoroughly. This paper should be of value to investigators who are interested in state of the art of metal powder metallurgy, particularly the MIM technology for biocompatible metal implant design and development.
In order to address slagging, fouling and high-temperature corrosion problems caused by alkali metals in Municipal Solid Waste (MSW), in-situ measurement of alkali metal in MSW incinerators is needed. The paper presents experimental measurements of temperatures and alkali metal concentrations in two MSW incinerators based on Flame Emission Spectroscopy (FES). Through the analysis of spontaneous emission spectra and a calibration procedure, the concentration of gas phase sodium (Na) and potassium (K), temperature and thermal radiation in the incinerator were in-situ measured by a portable spectral system simultaneously. Experimental results showed MSW composition has significant effect on the measured gaseous Na and K. Higher volatile content in MSW may enhance the alkali metal emission. Besides that, the released gaseous Na and K in the two incinerators are correlated with temperature in incinerators. The study provided a low cost and effective solution for in-situ measurement of temperature and alkali metal concentration in MSW incinerators.
The potential of selected materials in treating metal-rich acid mine drainage (AMD) has been investigated in a series of batch experiment. The efficiencies of both single and mixed substrates under two conditions i.e. low- and high-concentration solutions containing heavy metals were evaluated. Synthetic metal-containing AMD was used in the experiments treated using spent mushroom compost (SMC), ochre, steel slag (SS), and limestone. Different ratios of treatment materials were incorporated in the substrate mix and were tested in an anoxic condition. In the batch test, physicochemical parameters (pH, redox potential, total dissolved solids, conductivity, and Ca concentration) and heavy metals (Fe, Mn, Pb, Zn, and Al) were analysed. The mixed substrates have shown satisfactory performance in increasing pH with increasing Ca concentration and removing metals. It has been found that SS and ochre played an important role in the treatment of AMD. The results showed that the mixed substrates SM1 (i.e. 10% SMC mixed with 20% ochre, 30% steel slag, and 40% limestone) and SM2 (i.e. 20% SMC mixed with 30% ochre, 40% steel slag, and 10% limestone) were effective in increasing the pH from as low as 3.5-8.09, and removing heavy metals with more than 90% removal efficiencies.
Inverse vulcanized polysulfides have been used as low-cost and effective adsorbents to remediate heavy metals in wastewater. Inverse vulcanization introduces sustainable polysulfide synthesis by solving the rapid desulfurization problem of unstable polysulfides, and provides superior performance compared to conventional commercial adsorbents. The review discussed the brief applications of the inverse vulcanized polysulfides to remove heavy metal wastewater and emphasized the modified synthesis processes for enhanced uptake ratios. The characteristics of polysulfide adsorbents, which play a vital role during the removal process are highlighted with a proper discussion of the interaction between metal ions and polysulfides. The review paper concludes with remarks on the future outlook of these low-cost adsorbents with high selectivity to heavy metals. These polysulfide adsorbents can be prepared using a wide variety of crosslinker monomers including organic hydrocarbons, cooking oils, and agro-based waste materials. They have shown good surface area and excellent metal-binding capabilities compared to the commercially available adsorbents. Proper postmodification processes have enabled the benefits of repetitive uses of the polysulfide adsorbents. The improved surface area obtained by appropriate choice of crosslinkers, modified synthesis techniques, and regeneration through post-modification has made inverse vulcanized polysulfides capable of removing.
Heavy metals released by various industries are among the major pollutants found in water resources. In this research, biosorption technique was employed to remove cadmium (Cd2+) from an aqueous system using a novel biosorbent developed from okara waste (OW), a residue from soya bean-based food and beverage processing. Characterisation results revealed that the OW biosorbent contained functional groups such as hydroxyl-, carboxyl- and sulphur-based functional groups, and the surface of the biosorbent was rough with multiple fissures which might be the binding sites for the pollutant. The effects of dosage, solution pH, initial Cd2+ concentration, temperature and contact time were investigated using batch adsorption mode. The biosorption equilibrium and kinetic were best described by the Langmuir and Elovich models, respectively. The maximum biosorption capacities predicted by the Langmuir model were 10.91-14.80 mg/g at 30-70 °C, and the biosorption process was favourable as evident from 0 < RL < 1. The uptake of Cd2+ by the OW biosorbent was spontaneous and endothermic. The plausible biosorption mechanisms of this study could be ionic exchange, hydrogen bonding and electrostatic interactions. The Cd2+ loaded OW biosorbent could be regenerated using 0.4 M of HCl solution and regeneration was studied for 4 adsorption-desorption cycles. The present investigation supported that OW can be reused as a value-added biosorbent product for the removal of Cd2+ from the contaminated water.