Metals In Aqueous Solutions Research Articles

Composition-Dependent Morphostructural Properties of Ni–Cu Oxide Nanoparticles Confined within the Channels of Ordered Mesoporous SBA-15 Silica

NiO and NiO-CuO polycrystalline rodlike nanoparticles were confined and stabilized within the channels of ordered mesoporous SBA-15 silica by a simple and viable approach consisting in incipient wetness impregnation of the calcined support with aqueous solutions of metal nitrates followed by a mild drying step at 25 °C and calcination. As revealed by low- and high-angle XRD, N2 adsorption/desorption, HRTEM/EDXS and H2 TPR analyses, the morphostructural properties of NiO-CuO nanoparticles can be controlled by adjusting their chemical composition, creating the prerequisites to obtain high performance bimetallic catalysts. Experimental evidence by in situ XRD monitoring during the thermoprogrammed reduction indicates that the confined NiO-CuO nanoparticles evolve into thermostable and well-dispersed Ni-Cu heterostructures. The strong Cu-Ni and Ni-support interactions demonstrated by TPR and XPS were put forward to explain the formation of these new bimetallic structures. The optimal Ni-Cu/SBA-15 catalyst (i.e., Cu/(Cu+Ni) atomic ratio of 0.2) proved a greatly enhanced reducibility and H2 chemisorption capacity, and an improved activity in the hydrogenation of cinnamaldehyde, as compared with the monometallic Ni/SBA-15 or Cu/SBA-15 counterparts, which can be associated with the synergism between nickel and copper and high dispersion of active components on the SBA-15 host. The unique structure and controllable properties of both oxidic and metallic forms of Ni-Cu/SBA-15 materials make them very attractive for both fundamental research and practical catalytic applications.

A qualitative study of the effect of a counterion and polar environment on the structure and spectroscopic signatures of a hydrated hydroxyl anion

The results of the qualitative analysis of the effect of a counterion and polar environment on the structure and spectroscopic signatures of a hydrated hydroxyl anion based on DFT/M06-2X calculations in the polarizable cavity approximation reported in this work provide a tool to discriminate between the spectral signatures of the neutral, OH−·(nH2O) B+, and anionic, OH−·(nH2O), solvation clusters in aqueous solutions of alkali metal (B) hydroxides. These results demonstrate also that the precisions of the available experimental data and of the double harmonic approximation are insufficient to attribute the experimental spectral signatures to any specific cluster with the certain number of involved water molecules at least for 3 ≤ n ≤ 6.

Adsorption of Heavy Metal Ion from Aqueous Single Metal Solution by Aminated Epoxy-Lignin

This study investigated the adsorption of the heavy-metal ions Cu(II) and Pb(II) onto a lignin derivative. The lignin derivative was obtained by treating bagasse soda lignin with epichlorohydrin, and subsequently grafting an amine functional group by the Mannich reaction. The morphology of aminated epoxy-lignin was a layered structure with pores characterized by SEM. The heavy-metal ion adsorption data could be described well with the pseudo-first order model for Pb(II) ion and the pseudo-second order model for Cu(II) ion; diffusion was found to be the rate-limiting step when approaching equilibrium. FTIR spectroscopy was used to study the mechanism of heavy-metal adsorption by the derivatized lignin. The results show that the sites for adsorption are related to hydroxyl and amido groups.

The use of Crambe abyssinica seeds as adsorbent in the removal of metals from waters

This study aimed to evaluate the efficacy of crambe seeds (Crambe abyssinica Hochst) as adsorbent material in the removal of the toxic metals cadmium, lead and chromium from contaminated solutions. The byproduct was obtained from oil extraction of crambe seeds in a Soxhlet system. In kinetic tests, the adsorbent masses had varied in solutions containing the metals under pH 5.0 and 7.0. Metal concentrations were determined by flame atomic absorption spectrometry (FAAS). According to optimal conditions found, the adsorption assays were performed for obtaining the isotherms of each metal, which were linearized in agreement with the mathematical models of Langmuir and Freundlich. According to the obtained results, the adsorbent was effective in removing the assessed metals in aqueous solutions, being feasible its employment as an alternative material for the adsorption of metals, besides being a byproduct, which has undergone no prior treatment.

Structure of aqueous solutions of group IIIA metals perchlorates by near infrared spectroscopy

The state of water in aqueous solutions of group IIIA metal perchlorates at 25°C was studied by the IR spectroscopy in the range of 5400–7500 cm−1. The optical density values of the solution measured at different wavelengths were combined in a matrix of experimental data of the uniform dimension. The matrices were chemometrically analyzed. A number, spectra, and concentration profiles of the spectral forms existing in the solution were determined. By the principal component method, the IR spectra of the studied systems are grouped into the mathematical clusters according to the nature of the cation-water interaction in the solution. The combined use of the infrared spectroscopy and chemometric analysis showed that the structural changes in the solution predicted by the generalized phenomenological model are due to the existence and interconversion of the spectral forms.

Removal of lead(II) and zinc(II) ions from aqueous solutions by adsorption onto activated carbon synthesized from watermelon shell and walnut shell

Activated carbons from watermelon shell (GACW) and walnut shell (GACN) were synthesized through chemical activation with phosphoric acid 40 % w/w, as an alternative low-cost adsorbent for the removal of lead(II) and zinc(II) ions from aqueous solutions. The yield of production was 85 and 80 % for GACW and GACN respectively. To compare the differences and similarities between the two activated carbons the following tests were performed: surface and pore width with SEM, nitrogen adsorption isotherms at −196 °C (77 K), IR spectroscopy, TGA, point of zero charge (PZC) and Boehm titration. The GACN has 10 % more surface area (789 m2 g−1 for GACN and 710 m2 g−1 for GACW) and 13 % more pore volume than GACW. Also, GACN has a better resistance to high temperatures than GACW (the loss of mass at 900 °C was 20 % for GACN, while for GACW was 31 %). The effect of the initial concentration of lead(II) and zinc(II) ions on the adsorption process was studied in a batch process mode. To quantify the adsorption of lead and zinc adsorption isotherms of both metals in aqueous solution were performed for each carbon using analytic technique of atomic absorption. The adsorption isotherm data were better fitted by Langmuir model. Experimental results suggests that one gram of GACW adsorbs more milligrams of lead(II) and zinc(II) than one gram of GACN; it is suggest that the pore distribution is a significant variable in the adsorption process because GACW present mesopores and micropores, while GACN has only micropores. Also, the surface chemistry is an important variable in the adsorption process because GACW presents a lower pHPZC than GACN (3.05 for GACW and 4.5 for GACN) and the solution’s pH of each metal was adjusted in 4.5, for that it could be suggested that the electrostatic interactions were increased between the ion and the carbon surface.

Feasibility of anaerobic digested corn stover as biosorbent for heavy metal

Anaerobic digested (AD) corn stover collected from a lab-scale reactor was used as bioadsorbent to remove the heavy metal in aqueous solution. Effects of contact time and initial heavy metal concentrations on the removal process of Cu2+ and Cd2+ were investigated. The maximum adsorption capacities of AD corn stover obtained from Langmuir isotherm models were 83.3 and 50.0mg/g for Cu2+ and Cd2+, respectively. Fourier transform infrared spectroscopy (FTIR) was also used to investigate the surface characteristic of raw and heavy metal loaded AD corn stover.

Estimation of efficiency of DMSPN to protect cooling water systems from scale formation and corrosion

Despite many studies and publications on the development of effective stabilizers of scale formation and corrosion inhibitors, this problem is still topical. The most spread inhibitors of salt deposits are polyphosphate and diverse phosphonic acids. The disadvantage of polyphosphate is the capacity of hydrolysis at high temperatures and stimulation of biofouling. Phosphonic acids are expensive reagents. It is important that the substances, used as stabilizers of scale formation to be effective in protection of metals against corrosion in water. Phosphorus-containing complexons and their complexes with various metals in aqueous solutions are among the most promising inhibitors of corrosion of ferrous and non-ferrous metals. However, until now they are not very popular. Phosphonic acids can often be ineffective as inhibitors of corrosion of metals, and in some cases, they can encourage corrosion. The development of highly efficient scale formation and corrosion inhibitors and treatment of water will ensure efficient operation of heat-and-power equipment with the possibility to refuse from expensive and cumbersome systems of water softening and deaeration. The article presents the results of studies on the effectiveness of the DMSPN as a stabilizer of scale formation and a corrosion inhibitor of metal corrosion for resource-saving water circulation cooling systems. It was found that the DMSPN is a promising inhibitor for stabilizing treatment of water circulation cooling systems

Synthesis and potentiometric studies of novel aminomethylphosphinic acids and their complexation properties with transition metals in aqueous solution

Five novel aminomethylphosphinic acid ligands (L1–L5) have been synthesized and characterized. The pH-potentiometric technique was used for determining the dissociation constants (pK) of the compounds. The stabilizing ability of complexes of a novel chiral ligand of bis(aminomethyl)phosphinic acid (L1) with transition metals such as Co2+, Ni2+, Zn2+, Fe2+, Cu2+, Cd2+ and lanthanide ions La3+, Gd3+ in aqueous solutions have been studied by the pH-potentiometric technique. The complexation studies show that there is a significant difference between transition metals and lanthanide ions.

Evaluation of a novel chitosan polymer-based adsorbent for the removal of chromium (III) in aqueous solutions

Novel poly(vinyl alcohol)/citric acid/chitosan (PVA/CA/CHT, PCC) beads were prepared as an adsorbent for the removal of trivalent chromium (Cr3+) in aqueous solutions. PCC beads with different mass ratios (I, II, III, IV, V, ad VI) between PVA/CA/CHT were evaluated for the removal of Cr3+ ions to find an optimal stoichiometry of PCC beads, which indicated that the PCC bead (II) with the PVA/CA/CHT mass ratio of 1/5/1 showed the highest adsorption for Cr3+ ions. The surface characteristics of PCC beads (II) were determined by scanning electron microscopy using a field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR). The results obtained in this study implied that PCC bead (II) had an obviously rough and folded structure, and its spectrum manifested significant changes compared to those of PVA, CA and CHT. The sorption experiments were conducted to evaluate the performance of PCC beads (II) to adsorb Cr3+ ions in aqueous solutions. Results indicated that the Cr3+ ion sorption onto PCC beads (II) was highly pH-dependent with the maximum uptake at pH 6.0. The sorption kinetics data were well fitted by the pseudo-second-order equation with high regression coefficients. Sorption isotherm of PCC beads (II) was well described by Langmuir equation, with a maximum sorption at 41.5mg Cr/g PCC beads (II). Desorption studies were also carried out by the repeated sorption/desorption experiments. The high efficiency and reusability of PCC beads (II) make them an attractive sorbent for the removal of Cr3+ and possibly other metals in aqueous solutions.

Valorization of carbide lime waste, a by-product of acetylene manufacture, in wastewater treatment

Every year increasing amounts of industrial waste are generated worldwide. Depending on their characteristics, wastes can represent an important source of secondary raw materials in order to replace natural resources. The growing amount of carbide lime waste (CLW), a by-product of acetylene production, has resulted in environmental problems. In the present study, the potential use of CLW for wastewater treatment was investigated. The main characteristics of the CLW were determined. Chemical and X-ray diffraction analyses indicated that CLW was similar in chemical and mineralogical compositions to industrial lime, except for the presence of carbon in the waste. Morphological and elemental chemical analyses by scanning electron microscopy and energy dispersive X-ray spectrometry revealed that CLW particles differ from industrial lime by the presence of carbon formations. The use of CLW was evaluated in the treatment of Annaba city wastewater effluent. CLW was found to be the suitable for the treatment of Annaba city wastewater for an optimal dose of 850 mg L-1. Percentage removal efficiency for turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5) was found to be 96, 98.2, 90 and 84.5%, respectively. Residual turbidity in supernatant was 4.5 NTU and total residual bacteria was 68 CFU mL-1. Algerian effluent quality standards for TSS and COD were met after treatment. However, BOD5, bacterial level and pH were high, emphasizing the need of pH adjustment and secondary treatment for the Annaba city effluent. The precipitation of heavy metals with CLW has been shown to be successful in reducing the level of soluble heavy metals in aqueous solution. The removal of heavy metals was enhanced at pH ranges 10-11 for zinc, 9.2-11.6 for lead, 4-11.8 for iron and 7-11.8 for copper. The results revealed that CLW can be effectively used in wastewater treatment.

SAXS characterization of genetically engineered tobacco mosaic virus nanorods coated with palladium in the absence of external reducing agents

Genetic modifications of the tobacco mosaic virus (TMV) coat proteins allow for an increase in the selective deposition and controlled growth of different metals onto the surface of the virus, making it an ideal biotemplate for metal nanowire formation. In the current process, TMV2Cys is coated sequentially with multiple uniform layers of palladium metal in aqueous solution under very mild conditions. Palladium nanowires of 300nm in length and 30–40nm in diameter have been created with this process. Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) are used to characterize the thickness and uniformity of the metal surface. The TEM and SAXS results confirm that the final thickness of the palladium nanowires is controllable by varying the number of coating layers or the initial palladium concentration.

Soft-chemical treatment of transition-metal-containing layered double hydroxides and their application in porous materials

Layered double hydroxides (LDH) containing Co or Ni as the divalent cation and Al or Fe as the trivalent cation were prepared by hydrothermal treatment. The LDH phase containing Al can be prepared at a pH of ca. 7, whereas the LDH phase containing Fe can be prepared at pH 10. The chemical composition of the LDH was estimated by the calculation of the weighted mean electronegativity of the cations present in the aqueous metal solution. The decarbonated LDHs are intercalated by sodium dodecyl sulfate and can be exfoliated in 1-butanol solution by ultrasonication. The resulting LDH aggregates with a card-house structure that can then be deposited from these exfoliated colloidal solutions by sodium carbonate. For Ni/Al and Ni/Fe LDHs, in particular, the specific surface area and pore volume drastically increased owing to the card-house texture formed by exfoliation and redeposition.

Ion-pairing in aqueous solutions of peroxodisulfates

Abstract Probable values of the degree of ion-pairing (ion-association) of aqueous solutions of alkali metal and ammonium peroxodisulfates have been calculated for various estimated values of association constants, in dependence a) on the concentration of the binary solution, b) on the concentration of the other electrolyte in the polycomponent solution with the common ion, able or not able to form ion pair, and c) on the value of the activity quotient Qa. It followed that in the presence of another component with a common cation and neglecting the influence of activity coefficients, the ion-association degree of peroxodisulfate α > 0.5 in solutions with total molality mt > 0.1 mol kg-1; as mostly Qa < 1.0, the ion-association degree is even higher so that in such cases the alkali metal and ammonium peroxodisulfates can prevailingly behave as uni-univalent electrolytes. In agreement with these results, evaluation of the solubility of sodium, potassium and ammonium peroxodisulfates in some ternary and quaternary systems has been performed under the simplified assumption of a complete ion-association to MS2O81- ions. It has been shown that the mean deviations between the calculated and observed solubilities of the crystallizing components are almost equally low as under the assumption of a total dissociation of the corresponding substances. The results indicated that the prevailing ion-association of more concentrated solutions of peroxodisufates could be taken as an acceptable approach for the quantitative evaluation of physico-chemical behaviour of systems containing peroxodisulfates.

Biosorption of copper, zinc and cadmium using sodium hydroxide immersed Cymbopogon schoenanthus L. Spreng (lemon grass)

Studies were conducted to evaluate the performance of sodium hydroxide solution (NaOH) immersed lemon grass (ILG) adsorbing copper (Cu), zinc (Zn) and cadmium (Cd) in single-metal and multi-metal solutions, respectively. Parameters included pH, sorbent dosage and contact time. Fourier transform infrared (FTIR) spectrophotometer was used to elucidate ILG sorption mechanisms. Results indicated that sorption isotherms of ILG for all three metals were well described by Langmuir equation, with a maximum uptake at 13.93mg Cu, 15.87mg Zn and 39.53mg Cd per g ILG. The change of peaks in FTIR spectrum were observed after being immersed by 0.2M sodium hydroxide solutions (NaOH), which was likely to increase the number of sorption sites for metal uptake. Obtained results implied that ILG had a great potential for the removal of heavy metals in aqueous solutions.

Methods of using carbon nanotubes as filter media to remove aqueous heavy metals

Although carbon nanotubes (CNTs) are well known to have a strong affinity to various heavy metals in aqueous solution, little research has been dedicated to exploit their use in fixed-bed water treatment systems (e.g., trickling filters). In this work, batch sorption and fixed-bed experiments were conducted to examine the ability of functionalized multi-walled CNTs as filter media to remove two heavy metal ions (Pb2+ and Cu2+) from infiltrating water. Batch sorption experiments confirmed the strong sorption affinity of the CNTs for Pb2+ and Cu2+ in both single and dual metal solution systems. In addition, sonication-promoted dispersion of the CNT particles enhanced their heavy metal sorption capacity by 23.9–32.2%. For column experiments, laboratory-scale fixed-bed columns were packed with CNTs and natural quartz sand by three different packing: layered, mixed, and deposited. While all the three packing methods enhanced the fixed-bed filtering efficiency of Pb2+ and Cu2+ from single and dual metal systems, the CNT-deposited packing method was superior. Although the amount of the CNTs added into the fixed-bed columns was only 0.006% (w/w) of the sand, they significantly improved the fixed-bed’s filtering efficiency of Pb2+ and Cu2+ by 55–75% and 31–57%, respectively. Findings from this study demonstrate that functionalized multi-walled CNTs, together with natural sand, can be used to effectively and safely remove heavy metals from water.

Reaction pathways derived from DFT for understanding catalytic decomposition of formic acid into hydrogen on noble metals

Abstract Formic acid decomposition on noble metals is considered to be a potential method to produce CO-free hydrogen at near ambient temperatures. However, the reaction mechanism, as well as the key points, for HCOOH decomposition on noble metals in aqueous solution remains unclear at microscopic level. In the present work, we employed density functional theory (DFT) calculation to investigate HCOOH decomposition in gas and aqueous phases on four common noble metals (Pt, Pd, Rh, and Au). Based on the present theoretical calculation results and experimental results being available in literature, two reaction pathways were proposed to understand gas- and aqueous-phase HCOOH decomposition on the noble metals. The key points that determine the activities of the metals toward HCOOH decomposition into CO2 and H2 in aqueous solution are clarified. Furthermore, the proposed reaction mechanism can be well extended to interpret the excellent activity of Ag–Pd core–shell bimetallic catalyst for HCOOH decomposition in aqueous solution. It is expected the present reaction mechanisms would enable us to rationally design more active heterogeneous catalysts for HCOOH decomposition into CO-free H2 at relatively low temperatures.

Combination of electroreduction with biosorption for enhancement for removal of hexavalent chromium

Hexavalent chromium is one of the most toxic heavy metals in aqueous solutions. It has been well documented that the brown seaweed can be used as a promising biosorbent for the sequestration of this heavy metal from wastewater. However, the uptake of Cr(VI) is reportedly a rather slower process; the sorption equilibrium can only be established after a few days, much slower than a few hours for the trivalent chromium ion. In this study, we developed a novel technology of electrochemically assisted biosorption (ECAB) system for the enhancement of the treatment efficiency. It was found through our study that the removal efficiencies of Cr(VI) and total chromium were greatly enhanced by 48.1% and 51.3%, respectively, with the application of −1.0V in the ECAB system. The conversion of Cr(III) due to the electroreduction of Cr(VI) and the higher pH due to the cathodic H2 evolution created a favorable condition for the uptake of chromium onto the modified seaweed (MSW). The reduction and adsorption of Cr(VI) by MSW was proved to play a minor role in the removal. Both direct electroreduction and indirect electroreduction by atomic H* contributed to the reduction of Cr(VI).

Two Manifestations of the Passivity of the Metal in Aqueous Solution

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Adsorption of Cu (II) from Aqueous Single Metal Solutions by Bagasse Pith Chemically Modified with EDTA Dianhydride (EDTAD)

It was detail studied that the preparation of new chelating materials derived from bagasse pith for adsorption of Cu2+ ion. The bagasse pith was modified by the ethylenediaminetetraacetic dianhydride (EDTAD) and the mechanism of sorption property for heavy metal ion was studied. The FTIR was used to characterize the esterified pith(EP). The results show that the optimal conditions are 24 h of reaction time and 1.5 g of EDTAD dosage and the maximum adsorption capacity for Cu2+ is 76.76mg/g. The peaks at 1743.62 cm−1, 1598.59 cm−1,1408.06 cm−1 in FTIR suggest carbonyl functions in the materials. The Langmuir model can describe the process of adsorbing Cu2+onto EP.