Catalytic Role of Manganese Oxides in Prebiotic Nucleobases Synthesis from Formamide.

Origin of life processes might have begun with the formation of important biomonomers, such as amino acids and nucleotides, from simple molecules present in the prebiotic environment and their subsequent condensation to biopolymers. While studying the prebiotic synthesis of naturally occurring purine and pyrimidine derivatives from formamide, the manganese oxides demonstrated not only good binding for formamide but demonstrated novel catalytic activity. A novel one pot manganese oxide catalyzed synthesis of pyrimidine nucleobases like thymine is reported along with the formation of other nucleobases like purine, 9-(hydroxyacetyl) purine, cytosine, 4(3 H)-pyrimidinone and adenine in acceptable amounts. The work reported is significant in the sense that the synthesis of thymine has exhibited difficulties especially under one pot conditions and also such has been reported only under the catalytic activity of TiO2. The lower oxides of manganese were reported to show higher potential as catalysts and their existence were favored by the reducing atmospheric conditions prevalent on early Earth; thereby confirming the hypothesis that mineral having metals in reduced form might have been more active during the course of chemical evolution. Our results further confirm the role of formamide as a probable precursor for the formation of purine and pyrimidine bases during the course of chemical evolution and origin of life.

Biogenic magnetic nanocomposite of hydroxyapatite and dextran: synthesis, characterization, and enhanced removal of 2,4-D from aqueous environment.

In this study, a biogenic magnetic nanocomposite, HAP@DEX@MNP, using hydroxyapatite from eggshell waste and dextran was developed to efficiently remove 2,4-D from aqueous solutions. The magnetic nano biocomposite underwent rigorous characterization using a comprehensive suite of analytical techniques, including FTIR, XRD, FESEM, EDX, TEM, and VSM. FTIR analysis was used to validate the existence of pivotal functional groups, such as phosphate, carbonyl, hydroxyl, and iron oxide. XRD analysis verified both the crystalline nature of hydroxyapatite and the successful integration of dextran and hematite within the composite structure. FESEM and EDX examinations provided valuable insights into the surface morphology and elemental composition. TEM observations elucidated the existence of nano-sized particles underscoring the unique structural characteristics of the nanocomposite. Batch adsorption experiments were conducted under optimized conditions, highlighting the critical role of pH 2 for efficient 2,4-D removal. The mechanisms driving the binding of 2,4-D to HAP@DEX@MNP were found to encompass diverse interactions, encompassing electrostatic forces, hydrogen bonding, π-π interactions, and van der Waals forces. Adsorption isotherm studies revealed both monolayer and multilayer adsorption, with the Langmuir and Freundlich models fitting well, indicating a maximal adsorption capacity of 217.39 µg/g at 25 °C. Kinetic investigations supported the pseudo-second-order model for efficient adsorption dynamics, and thermodynamic analysis emphasized the versatility of HAP@DEX@MNP across different temperatures. Importantly, the study highlighted the remarkable regenerative capacity of the nanocomposite using a 0.1 M NaOH solution, positioning it as an environmentally friendly option for water treatment. In conclusion, HAP@DEX@MNP holds significant potential for diverse applications in addressing global water treatment and environmental challenges.

Removal of emergent pollutants: A review on recent updates and future perspectives on polysaccharide-based composites vis-à-vis traditional adsorbents.

There is a growing incidence in the presence of emergent pollutants like the pesticides and pharmaceuticals in water bodies. The matter of environmental concern is their synthetic and persistent nature which has resulted in induced toxicity/damaging effect to the vital functioning of the different organs in the aquatic community. Traditional adsorbents have exhibited limitations like low stability and minimum reuse ability. Composites of such adsorbents with polysaccharides have demonstrated distinct features like improved surface area, porosity, adsorptivity; improved reusability and structural integrity; improved mechanical strength, thermal stability when applied for the removal of the emergent pollutants. The biocompatibility and biodegradability of such fabricated composites is established; thereby making the water treatment process cost effective, sustainable and environmentally friendly. The present review has dealt with an in-depth, up-dated literature compilation of traditional as well as polysaccharide based composite adsorbents and addressed their performance evaluation for the removal of pharmaceuticals and pesticides from wastewater. A comparative study has revealed the merits of polysaccharide based composites and discussions have been made with a focus on future research directions in the related area.

Fabrication of nano-biocomposite for the removal of Eriochrome Black T and malachite green from aqueous solution: isotherm and kinetic studies.

The increasing generation of toxic dye wastewater from various enterprises continues to be a serious public health issue and happens to be of environmental concern, posing a significant challenge to existing conventional water treatment facilities. Malachite green (MG) and Eriochrome Black T (EBT) are extremely hazardous and carcinogenic substances; hence it is crucial to remove them from water bodies. A well-known cleaner, more economical, and environmentally friendly treatment method is adsorption. The kind of adsorbent material employed determines how well the treatment procedure works. A physiologically compatible nanocomposite adsorbent (HAP@CT@MNP) was fabricated from laboratory synthesized hydroxyapatite (HAP) and magnetite (MNP) for its application in the wastewater remediation process. The ability of the fabricated nanocomposite to remove the harmful dyes EBT and MG from a simulated wastewater was evaluated. The impact of operational parameters including pH, adsorbate concentration, adsorbent dose, contact time, and temperature was examined to gauge the maximum adsorption capacity of the developed nanocomposite. The optimum pH for the eradication of EBT and MG were found to be 3 and 7.4, respectively. The maximum capacity evaluated was 222 mg/g and 500 mg/g at room temperature and at contact time of 50 and 40 min respectively. The binding of either EBT or MG followed the monolayer Langmuir model and kinetic studies revealed the suitability of pseudo-second-order model. Studies using spectroscopy and isotherm modeling showed that the main mechanism controlling the adsorption of EBT and MG onto HAP@CT@MNP is physisorption. The efficacy of the adsorbent to be reused with 8% loss in its efficiency reveals the economic viability of HAP@CT@MNP. The current work showed that a biocompatible nanocomposite could be successfully fabricated and used as an enhanced adsorbent for the quick and effective removal of the toxic dyes EBT and MG from wastewater.

Chemically activated carbon from lignocellulosic wastes for heavy metal wastewater remediation: Effect of activation conditions.

Chemical activation is known to induce specific surface features of porosity and functionality which play a definite role in enhancing the adsorptive potential of the developed activated carbons. Different conditions of temperature, time, reagent type and impregnation ratio were applied on sawdust precursor and their effect on the physical, surface chemical features and finally on the adsorption potential of the developed activated carbons were analysed. Under activation conditions of 600°C, 1hr, 1:0.5 ratio, ZnCl2 impregnated carbon (CASD_ZnCl2) resulted in microporosity while KOH impregnation (CASD_KOH) yielded a carbon having a wider pore size distribution. The surface chemistry revealed similar functionalities. At same pH, temperature and adsorbate concentrations, CASD_KOH demonstrated better adsorption potential (1.06mmoles/g for Cd2+ and 1.61mmoles/g for Ni2+) in comparison to CASD_ZnCl2 (0.23mmoles/g and 0.33mmoles/g for Cd2+ and Ni2+ respectively). Other features were a short equilibrium time of 60mins and an adsorbent dose of 0.2g/L for the CASD_KOH in comparison to CASD_ZnCl2 (equilibrium time of 150min and dosage of 0.5g/L). The nature of interactions was physical for both adsorbents and pore diffusion mechanisms were operative. The results reveal the potentiality of chemical activation so as to achieve the best physico-chemical properties suited for energy efficient, economical and eco-friendly water treatment.

Potential of activated carbon from waste rubber tire for the adsorption of phenolics: effect of pre-treatment conditions.

Rubber tire activated carbon modification (RTACMC) and rubber tire activated carbon (RTAC) were prepared from waste rubber tire by microwave assisted chemical treatment and physical heating respectively. A greater improvement in porosity and total pore volume was achieved in RTACMC as compared to that of RTAC. But both have a predominantly mesoporous structure. Under identical operating conditions, an irradiation time of 10 min, chemical impregnation ratio of 1.50 and a microwave power of 600 W resulted in maximizing the efficiency of RTACMC for p-cresol (250 mg/g) at a contact time of 90 min while RTAC showed a 71.43 mg/g adsorption capacity at 150 min. Phenol, due to its higher solubility was adsorbed to a lesser extent by both adsorbents. Physical nature of interactions, pore diffusion mechanism and exothermicity of the adsorption process was operative in both adsorbents. The outcomes support the feasibility of preparing high quality activated carbon from waste rubber tire by microwave assisted chemical activation.

Adsorptive removal of dyes from aqueous solution onto carbon nanotubes: a review.

Adsorption is a widely used technique for the separation and removal of pollutants from wastewaters. Carbon nanotubes (CNTs) are emerging as potential adsorbents because of its well defined cylindrical hollow structure, large surface area, high aspect ratios, hydrophobic wall and easily modified surfaces. In this review, dye adsorption capability of CNTs and CNT based composites from aqueous system has been compiled. This article provides the information about the defect, adsorption sites on CNTs and batch adsorption studies under the influence of various operational parameters such as contact time, solution pH, temperatures etc. and deals with mechanisms involved in adsorption of dyes onto CNTs. From the literature reviewed, it is observed that single walled carbon nanotubes (SWCNTs) show higher adsorption capacity than multi walled carbon nanotubes (MWCNTs) and functionalized and CNT composite have better sorption capacity than as grown CNTs. It is evident from the literature that CNT based nanosorbents have shown good potential for the removal of dyes from aqueous solution. However, still more research work should be focused on the development of cost effective, higher efficient and environmental friendly CNT based nanosorbents for their commercial applications.

Photodegradation of hazardous dye quinoline yellow catalyzed by TiO2.

The photocatalytic degradation of hazardous dye quinoline yellow, employing a heterogeneous photocatalytic process using TiO(2) photocatalyst irradiated with 6 W UV light source tungsten lamp, has been studied. The effect of various operational parameters, i.e., dye concentration, photocatalyst concentration, pH of the solution, substrate concentration, and electron acceptor such as hydrogen peroxide on the degradation rate of aqueous solutions of quinoline yellow has been examined. The disappearance of the dye follows a pseudo first order kinetics according to the Langmuir Hinshelwood model. Results show that the use of an efficient photocatalyst and the selection of optimal operational parameters may lead to complete decolorization and to sustainable decrease in the chemical oxygen demand (COD) of the dye waste water.

Photo-catalytic degradation of toxic dye amaranth on TiO(2)/UV in aqueous suspensions.

The photo-catalytic degradation of an azo dye - Amaranth (AM) - has been investigated in TiO(2)/UV aqueous suspensions. The results obtained from the experiments during H(2)O(2)/TiO(2) addition show that the highest decolorization rate is provided by the combination of (UV+TiO(2)+H(2)O(2)). The decolorization efficiencies were 17%, 26%, 38% and 64% in the runs UV, UV+H(2)O(2), UV+TiO(2) and (UV+TiO(2)+H(2)O(2)) after approximately 100 min illumination periods, respectively. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. Different experimental conditions, such as temperature, pH and presence of electron acceptor were investigated. The temperature effect was investigated at the range of 293-313 K and it was observed that decolorization rate increased by the increase in temperature. Chemical oxygen demand and dye absorbance of the photodegraded dye solution substantially decreased. Effect of pH was also investigated and it was observed that the lower the pH the higher the degradation. In addition, an enhancement in the photodegradation rate was observed by the addition of hydrogen peroxide as an electron acceptor. The adsorption trends of Amaranth at various initial concentrations followed the Langmuir isotherm trend. This work adds to the global discussion on the role of the advanced oxidation processes in water treatment.

Pesticides removal from waste water by activated carbon prepared from waste rubber tire.

Waste rubber tire has been used for the removal of pesticides from waste water by adsorption phenomenon. By applying successive chemical and thermal treatment, a basically cabonaceous adsorbent is prepared which has not only a higher mesopore, macropore content but also has a favorable surface chemistry. Presence of oxygen functional groups as evidenced by FTIR spectra along with excellent porous and surface properties were the driving force for good adsorption efficiency observed for the studied pesticides: methoxychlor, methyl parathion and atrazine. Batch adsorption studies revealed maximum adsorption of 112.0 mg g(-1), 104.9 mg g(-1) and 88.9 mg g(-1) for methoxychlor, atrazine and methyl parathion respectively occurring at a contact time of 60 min at pH 2 from an initial pesticide concentration of 12 mg/L. These promising results were confirmed by column experiments; thereby establishing the practicality of the developed system. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the adsorbent with a higher adsorption capacity than most other adsorbents. The adsorption equilibrium data obey Langmuir model and the kinetic data were well described by the pseudo-first-order model. Applicability of Bangham's equation indicates that diffusion of pesticide molecules into pores of the adsorbent mainly controls the adsorption process. Spontaneous, exothermic and random characteristics of the process are confirmed by thermodynamic studies. The developed sorbent is inexpensive in comparison to commercial carbon and has a far better efficiency for pesticide removal than most other adsorbents reported in literature.

A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waste rubber tire and activated carbon for a hazardous azo dye--Acid Blue 113.

A mesoporous carbon developed from waste tire rubber, characterized by chemical analysis, FTIR, and SEM studies, was used as an adsorbent for the removal and recovery of a hazardous azo dye, Acid Blue 113. Surface area, porosity, and density were determined. The adsorption of the dye over the prepared adsorbent and a commercial activated carbon was achieved under different pH, adsorbate concentration, sieve size, adsorbent dosage, contact time and temperature conditions. Langmuir and Freundlich adsorption isotherm models were applied and thermodynamic parameters were calculated. Kinetic studies indicated that the adsorption process follow first order kinetics and particle diffusion mechanisms are operative. By percolating the dye solution through fixed-bed columns the bulk removal of the Acid Blue 113 was carried out and necessary parameters were determined to find out the percentage saturation of both the columns. Recovery of the dye was made by eluting 0.1 M NaOH through the column.

Electrochemical Analysis of Some Toxic Metals by Ion-Selective Electrodes.

An overview of potentiometric sensors that are capable of detecting toxic heavy metal ions in environmental samples is presented and discussed. Notwithstanding the tremendous work performed so far, it is obvious that still several limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. A survey on important advances in potentiometric sensors with regard to high selectivity, lower detection limit, fast response time, and on-line environmental analysis is presented in this review article. [Supplemental materials are available for this article. Go to the publisher's online edition of Critical Reviews in Analytical Chemistry to view the free supplemental file.].

Adsorption-desorption studies of indigocarmine from industrial effluents by using deoiled mustard and its comparison with charcoal.

Deoiled mustard obtained from local oil mills has been used as an inexpensive and effective adsorbent for the removal of indigocarmine dye from industrial effluents. The influence of various factors on the adsorption capacity has been studied by batch experiments. The adsorption studies validate both Langmuir and Freundlich adsorption isotherms. Thermodynamic parameters such as DeltaG degrees, DeltaH degrees, and DeltaS degrees for the adsorption process were calculated, which indicated the feasibility of the adsorption process. Desorption profiles revealed that a significant portion (85%) could be desorbed from deoiled mustard by using 30% glycerol as eluting agent.

Biosorption of nickel onto treated alga (Oedogonium hatei): Application of isotherm and kinetic models.

Oedogonium hatei was developed into an effective and efficient adsorbent for the removal of Ni(II) ions from aqueous solution. The adsorption studies of untreated and treated algal biomass (with 0.1M HCl) were compared in batch mode. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature and the Langmuir and Freundlich isotherms were found applicable in terms of relatively high regression values. The maximum monolayer adsorption capacity of the biosorbents (untreated and acid-treated algae), as obtained from the Langmuir adsorption isotherm, was found to be 40.9 and 44.2mg/g, respectively at 80min contact time, 5.0 pH, 0.7g/L algal dose, and 298K temperature. The thermodynamic parameters showed that the adsorption of Ni(II) ions onto algal biomass was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption followed both first- and second-order rate equations and the process involving the rate-controlling step is complex involving boundary layer as well as intraparticle diffusion processes. The FTIR results of algal biomass showed that biomass has different functional groups and these functional groups are able to react with metal ion in aqueous solution. Biosorbent could be regenerated using 0.1M NaOH solution, with up to 70% recovery. The performance of this biosorbent was then compared with many other reported biosorbents for nickel removal and it was observed that the proposed adsorbent is effective in terms of its performance.

Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry waste material.

Low cost fertilizer industry waste material called carbon slurry, produced in generators of fuel oil-based industrial generators, was converted into an effective and efficient adsorbent for the removal of hexavalent chromium(VI) from aqueous solutions. The waste was chemically treated, activated, characterized, and used for the adsorption of chromium. The work involves batch experiments to investigate the effect of contact time, pH, temperature, concentration, and adsorbent dose on the extent of adsorption by carbon slurry. The maximum adsorption was found at 70min, 2.0 pH, 4.0g/L dose, and 303K temperature. Maximum adsorption capacity (15.24mg/g) of Cr(VI) on carbon slurry was observed at 100mg/L initial Cr(VI) concentration. Langmuir and Freundlich adsorption isotherm models were applied to analyze adsorption data, and both were found to be applicable to this adsorption system, in terms of relatively high regression values. Thermodynamic parameters showed that the adsorption of Cr(VI) onto carbon slurry was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption was found to follow the pseudo-second-order rate equation. Column studies have been carried out to compare these with the batch capacities. The recovery of Cr(VI) and chemical regeneration of the spent column have also been tried. In all, the results indicated that the adsorbent used in this work proved to be effective material for the treatment of chromium-bearing aqueous solutions.