Porous material based on modified carbon and the effect of pore size distribution on the adsorption of methylene blue dye from an aqueous solution

Carbon porous materials obtained through KOH activation of a furfural + hydroquinone + urotropine mixture were applied as adsorbent for the remediation of methylene blue (MB). The impact of porous structure with special attention to pore size distribution along with well-known pore volume and specific surface area on the remediation of MB was well investigated and elucidated. Findings obtained revealed that pore size distribution plays a crucial role in the liquid-phase adsorption of organic dyes like MB. By varying the synthesis mode parameters, in particular, the activating agent/precursor mass ratio, with the composition and initial components ratios remaining unchanged, samples with different pore size distribution were obtained. It was found that the material predominantly containing pores with an average equivalent diameter of ~ 3.5 nm appears to be the efficient MB adsorbent. The resulting highly porous carbon materials demonstrated high MB adsorption capacity (up to 2555 mg/g). Furthermore, to fully elucidate the adsorption mechanisms occurring on the obtained materials, a comprehensive mathematical processing of experimental data was performed out using the known kinetic and diffusion models (pseudo-first- and pseudo-second order, and intraparticle diffusion), as well as adsorption equilibrium isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich).It can be concluded that the porous carbon materials obtained and described in the present work are effective adsorbents for the removal of MB and may possess great potential for the treatment of dye-containing wastewater.

Nanoporous carbon materials as a sustainable alternative for the remediation of toxic impurities and environmental contaminants: A review

Due to rapidly deteriorating water resources, the world is looking forward to a sustainable alternative for the remediation of noxious pollutants such as heavy metals and organic and gaseous contaminants. To address this global issue of environmental pollution, nanoporous carbon materials (NPCMs) can be used as a one-stop solution. They are widely applied as adsorbents for many toxic impurities and environmental contaminants. The present review provides a detailed overview of the role of different synthesis factors on the porous characteristics of carbon materials, activating agents, reagent-precursor ratio and their potential application in the remediation. Findings revealed that synthetic parameters result in the formation of microporous NPCMs (S_BET: >4000 m³/g; V_Total (cm³/g) ≥ 2; V_Micro (cm³/g) ≥ 1), micromesoporous (S_BET: >2500 m³/g; V_Total (cm³/g) ≥ 1.5; V_Micro (cm³/g) ≥ 0.7) and mesoporous (S_BET: >2500 m³/g; V_Total (cm³/g) ≥ 1.5; V_Micro (cm³/g) ≥ 0.5) NPCMs. Moreover, it was observed that a narrow pore size distribution (0.5-2.0 nm) yields excellent results in the remediation of noxious contaminants. Further, chemical activating agents such as NaOH, KOH, ZnCl₂, and H₃PO₄ were compared. It was observed that activating agents KОН, H₃PO₄, and ZnCl₂ were generally used and played a significant role in the possible large-scale production and commercialization of NPCMs. Thus, it can be interpreted that with a well-planned strategy for the synthesis, NPCMs with a "tuned" porosity for a specific application, in particular, microporosity for the accumulation and adsorption of energetically important gases (CO₂, CH₄, H₂), micro-mesoporosity and mesoporosity for high adsorption capacity for towards metal ions and a large number of dyes, respectively.

High-Speed and High-Capacity Removal of Methyl Orange and Malachite Green in Water Using Newly Developed Mesoporous Carbon: Kinetic and Isotherm Studies

A novel mesoporous carbon nanostructured material was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, thermogravimetry, and X-ray diffractometry. The material demonstrated high-speed and high-adsorption capacities of 827.5 and 2484.5 mg g^-1 for methyl orange (MO) and malachite green (MG) dyes in 10 min. The kinetic data were fitted to pseudo-first- and pseudo-second-order, external and intraparticle diffusion, and Elovich models, whereas the isotherm data were adjusted to the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Langmuir-Freundlich isotherms (Sips). It was found that MO and MG adsorption was limited by chemical interactions and mixed diffusion. Besides, the physical process was elucidated through free energy values (E = 2.56 and 0.049 kJ mol^-1 for the MO and MG, respectively). Methyl orange adsorption mostly occurred through ion exchange and electrostatic interactions, and at lower MO concentrations, through chemical interactions and surface complexation as well. Malachite green adsorption took place only on lower-energy sites. Thus, it can be concluded that the adsorbent proposed herein possessed high-speed and high-adsorption capacity. Therefore, it can be considered as promising in removing the reported dye pollutants.

Graphene based adsorbents for remediation of noxious pollutants from wastewater

The contamination of water resources with noxious pollutants is a serious issue. Many aquatic systems are contaminated with different toxic inorganic and organic species; coming to wastewater from various anthropogenic sources such as industries, agriculture, mining, and domestic households. Keeping in view of this, wastewater treatment appears to the main environmental challenge. Adsorption is one of the most efficient techniques for removing all most all types of pollutants i.e. inorganics and organics. Nowadays, graphene and its composite materials are gaining importance as nano adsorbents. Graphene; a two-dimensional nanomaterial having single-atom graphite layer; has attracted a great interest in many application areas (including wastewater treatment) due to its unique physico-chemical properties. The present paper is focused on the remediation of noxious wastes from wastewater using graphene based materials as adsorbents, and it contains all the details on materials - i.e., from their synthesis to application in the field of wastewater treatment (removal of hazardous contaminants of different chemical nature - heavy and rare-earth metal ions, and organic compounds - from wastewater effluents. The efficiency of the adsorption and desorption of these substances is considered. Certainly, this article will be useful for nano environmentalist to design future experiments for water treatment.

Water treatment by new-generation graphene materials: hope for bright future

Water is the most important and essential component of earth's ecosystem playing a vital role in the proper functioning of flora and fauna. But, our water resources are contaminating continuously. The whole world may be in great water scarcity after few decades. Graphene, a single-atom thick carbon nanosheet, and graphene nanomaterials have bright future in water treatment technologies due to their extraordinary properties. Only few papers describe the use of these materials in water treatment by adsorption, filtration, and photodegradation methods. This article presents a critical evaluation of the contribution of graphene nanomaterials in water treatment. Attempts have been made to discuss the future perspectives of these materials in water treatment. Besides, the efforts are made to discuss the nanotoxicity and hazards of graphene-based materials. The suggestions are given to explore the full potential of these materials along with precautions of nanotoxicity and its hazards. It was concluded that the future of graphene-based materials is quite bright.

Leachability of major and minor elements from soils and sediments of an abandoned coal mining area in Southern Brazil

Leachability of major and trace elements from sediment and soil samples of an abandoned coal mining area in southern Brazil was assessed by titration and pH-stat tests according to the SR002.1 and CEN/TS 14429 protocols. Major (Al, Fe, Ca, Mg, and Mn) and trace (Cu, Zn, As, Ni, Pb, Cd, and Hg) elements were quantified in aqueous extracts. Acid and base neutralizing capacity values and pH changes after the addition of certain acid/base amounts were estimated. In general, a decrease in the major metal leaching at pH < 4.0 and an increase at pH > 8.0 was observed. The response to the acid and base additions confirmed that strong acids can cause an effect on Ca- and Mg-bearing silicate phases and Mn oxides, and strong bases can only affect Ca silicates. At pH < 5.0, higher extractability was found for Cu, Zn, Ni, Pb, and Cd. Considering that the samples showed sharp pH changes after acid additions and released major and trace metal into the solution at greater rates, high metal contamination risks can be assumed for the studied area.

Cadmium mobility in sediments and soils from a coal mining area on Tibagi River watershed: environmental risk assessment

The risk of cadmium contamination in the Tibagi River watershed (Parana State, Brazil) affected by past coal mining activities was assessed through sorption-desorption modeling for sediment and soil samples. The acidic character of the samples resulted in more competition between the cadmium ions and protons, thereby influencing the cadmium sorption-desorption. The sorption isotherms were fitted to the Langmuir and Freundlich single models and to the dual-site Langmuir-Freundlich (or Sips) model. The single-site models indicated a low-energy character of sorption sites on the sample sorption sites, whereas the dual-site model explained the availability of higher-affinity and lower-affinity non-specific sites. The correlation of the sorption and desorption constants with the physicochemical and mineralogical characteristics of the samples showed that the cadmium sorption behavior was significantly affected by the pH, point of zero charge, and also by the magnesium, aluminum, calcium and manganese amounts. Besides, the desorption rate and hysteresis index suggested a high risk of cadmium mobilization along the Tibagi River basin.

Examination of competitive lanthanide sorption onto smectites and its significance in the management of radioactive waste

The competitive effect of La and Lu (analogues of radionuclides appearing in radioactive waste) in the sorption in four smectites was examined. Sorption and desorption distribution coefficients (K(d); K(d,des)), and desorption rates (R(des)) were determined from batch tests in two media: deionized water and, to consider the influence of cement leachates, 0.02 mol L(-1) Ca. The competitive effect was lower when high-affinity sites were available, as in the water medium at the lowest range of initial lanthanide concentration, with high K(d) for La and for Lu (5-63×10(4) L kg(-1)). Lower K(d) was measured at higher initial concentrations and in the Ca medium, where Lu showed a stronger competitive effect. This was confirmed by fitting the sorption data to a two-solute Langmuir isotherm. The desorption data indicated that sorption was virtually irreversible for the scenarios with high sorption, with an excellent correlation between K(d) and K(d,des) (R(2) around 0.9 for the two lanthanides). Assuming that radioactive waste is a mixture of radionuclides, and that Ca ions will be provided by the cement leachates, this would reduce the retention capacity of clay engineered barriers.

Reversibility of La and Lu sorption onto smectites: implications for the design of engineered barriers in deep geological repositories

The sorption reversibility of La and Lu (considered as actinide analogues) onto a set of smectites (bentonite FEBEX; hectorite, HEC; MX80; saponite, SAP; Otay montmorillonite, SCa-3; and Texas montmorillonite, STx-1) was studied to estimate actinide retention by smectites that are candidates for use as engineered barriers in deep geological repositories. The sorption distribution coefficients (K(d)) and the reversibility parameters (desorption distribution coefficients (K(d,des)), adjusted distribution coefficients (K(d,adj)), and desorption rates (R(des))) were determined from batch tests in two ionic media: deionized water and Ca 0.02 mol L(-1). The latter simulates possible conditions due to the presence of concrete leachates. The results varied greatly depending on the ionic medium, the lanthanide concentration and the clay structure. The high values of K(d,des) obtained (up to 1.1 x 10(5) and 9.2 x 10(4) L kg(-1) for La and Lu in water, and 2.8 x 10(4) and 4.1 x 10(4)L kg(-1) for La and Lu in the Ca medium) indicate the suitability of the tested smectites for lanthanide (and therefore, actinide) retention. Based on all the data, SCa-3, HEC and FEBEX clays are considered the best choices for water environments, whereas in Ca environments the suitable clays depended on the lanthanide considered.