Estimation of equilibrium times and maximum capacity of adsorption of heavy metals by E. crassipes (review)

Bacterial Cellulose-Derived Sorbents for Cr (VI) Remediation: Adsorption, Elution, and Reuse

The search for adsorbents that are non-toxic and low cost with a high adsorption capacity and excellent recyclability is a priority to determine the way to reduce the serious environmental impacts caused by the discharge of effluents loaded with heavy metals. Bacterial cellulose (BC) biomass has functional groups such as hydroxyl and carbonyl groups that play a crucial role in making this cellulose so efficient at removing contaminants present in water through cation exchange. This research aims to develop an experimental process for the adsorption, elution, and reuse of bacterial cellulose biomass in treating water contaminated with Cr (VI). SEM images and the kinetics behavior were analyzed with pseudo-first- and pseudo-second-order models together with isothermal analysis after each elution and reuse process. The adsorption behavior was in excellent agreement with the Langmuir model along with its elution and reuse; the adsorption capacity was up to 225 mg/g, adding all the elution processes. This study presents a novel approach to the preparation of biomass capable of retaining Cr (VI) with an excellent adsorption capacity and high stability. This method eliminates the need for chemical agents, which would otherwise be difficult to implement due to their costs. The viability of this approach for the field of industrial wastewater treatment is demonstrated.

Design of a sustainable system for wastewater treatment and generation of biofuels based on the biomass of the aquatic plant Eichhornia Crassipes

Colombia’s continuous contamination of water resources and the low alternatives to produce biofuels have affected the fulfillment of the objectives of sustainable development, deteriorating the environment and affecting the economic productivity of this country. Due to this reality, projects on environmental and economic sustainability, phytoremediation, and the production of biofuels such as ethanol and hydrogen were combined. The objective of this article was to design and develop a sustainable system for wastewater treatment and the generation of biofuels based on the biomass of the aquatic plant Eichhornia crassipes. A system that simulates an artificial wetland with live E. crassipes plants was designed and developed, removing organic matter contaminants; subsequently, and continuing the sustainability project, bioreactors were designed, adapted, and started up to produce bioethanol and biohydrogen with the hydrolyzed biomass used in the phytoremediation process, generating around 12 g/L of bioethanol and around 81 ml H2/g. The proposed research strategy suggests combining two sustainable methods, bioremediation and biofuel production, to preserve the natural beauty of water systems and their surroundings.

Design of a sustainable system for wastewater treatment and generation of biofuels based on the biomass of the aquatic plant Eichhornia Crassipes

Colombia's continuous contamination of water resources and the low alternatives to produce biofuels have affected the fulfillment of the objectives of sustainable development, deteriorating the environment and affecting the economic productivity of this country. Due to this reality, projects on environmental and economic sustainability, phytoremediation, and the production of biofuels such as ethanol and hydrogen were combined. The objective of this article was to design and develop a sustainable system for wastewater treatment and the generation of biofuels based on the biomass of the aquatic plant Eichhornia crassipes. A system that simulates an artificial wetland with live E. crassipes plants was designed and developed, removing organic matter contaminants; subsequently, and continuing the sustainability project, bioreactors were designed, adapted, and started up to produce bioethanol and biohydrogen with the hydrolyzed biomass used in the phytoremediation process, generating around 12 g/L of bioethanol and around 81 ml H2/g. The proposed research strategy suggests combining two sustainable methods, bioremediation and biofuel production, to preserve the natural beauty of water systems and their surroundings.

The Design of a Process for Adsorbing and Eluting Chromium (VI) Using Fixed-Bed Columns of E. crassipes with Sodium Tripolyphosphate (TPP)

Proper water resource management is a critical global objective, both privately and in business, due to the continuous deterioration of this valuable resource. Scientific research in environmental sciences has made significant progress in the development and achievements of treatment. The use of transformed E. crassipes biomass with sodium tripolyphosphate (TPP) can help to achieve this important goal. The objective of this study was to develop an experimental process for the continuous adsorption and elution of chromium (VI) using fixed-bed columns of E. crassipes biomass modified with sodium tripolyphosphate (TPP). Additionally, design tools were created, and economic viability was assessed by analyzing adsorption capacity indicators and unit production costs of different biomasses. Treatment systems were designed and constructed to remove chromium from tannery wastewater, ensuring that the levels were below the current environmental regulations of 0.05 mg/L Cr(VI). The biomass had an adsorption capacity of 98 mg/g and was produced at a low cost of 8.5 dollars. This resulted in an indicator of 11.5 g Cr(VI)/(USD) when combined with the elution processes. The proposed strategy, which utilizes entirely green technologies, enables the recovery and valorization of water resources. This makes it an effective tool for the circular economy.

The Design of a Sustainable Industrial Wastewater Treatment System and The Generation of Biohydrogen from E. crassipes

Water scarcity is a significant global issue caused by the prolonged disregard and unsustainable management of this essential resource by both public and private bodies. The dependence on fossil fuels further exacerbates society's bleak environmental conditions. Therefore, it is crucial to explore alternative solutions to preserve our nation's water resources properly and promote the production of biofuels. Research into the utilization of E. crassipes to remove heavy metals and generate biofuels is extensive. The combination of these two lines of inquiry presents an excellent opportunity to achieve sustainable development goals. This study aims to develop a sustainable wastewater treatment system and generate biohydrogen from dry, pulverized E. crassipes biomass. A treatment system was implemented to treat 1 L of industrial waste. The interconnected compartment system was built by utilizing recycled PET bottles to generate biohydrogen by reusing the feedstock for the treatment process. The production of biological hydrogen through dark fermentation, using biomass containing heavy metals as a biohydrogen source, was studied. Cr (VI) and Pb (II) levels had a low impact on hydrogen production. The uncontaminated biomass of E. crassipes displayed a significantly higher hydrogen yield (81.7 mL H2/g glucose). The presence of Cr (IV) in E. crassipes leads to a decrease in biohydrogen yield by 14%, and the presence of Pb (II) in E. crassipes leads to a decrease in biohydrogen yield of 26%. This work proposes a strategy that utilizes green technologies to recover and utilize contaminated water. Additionally, it enables the production of bioenergy with high efficiency, indirectly reducing greenhouse gases. This strategy aligns with international programs for the development of a circular economy.

Design and Development of a Pilot-Scale Industrial Wastewater Treatment System with Plant Biomass and EDTA

The impact generated by the indiscriminate disposal of heavy metals into the different bodies of water is not only environmental but also social due to the health effects it produces in several organisms, including ourselves. Therefore, treatment systems around the world are the subject of continuous research to find treatment systems that are economical, efficient, and easy to implement in the industries that generate these increasingly harmful impacts on society and the environment in general. One way to design and develop systems of water treatment is that which takes advantage of the waste generated, such as the waste from the E. crassipes plant. The conditions of this plant make it perfect due to its abundant biomass and important content of cellulose and hemicellulose. Nevertheless, in almost all the investigations that characterize the way in which the biomass of this plant adsorbs heavy metals, it does so under laboratory conditions, being very far from the reality of industrial discharges. The objective of this project is to design and develop a pilot-scale industrial wastewater treatment system with plant biomass and EDTA. Three pilot-scale systems were built with EDTA-modified biomass in different concentrations, giving the parameters of the design for the development of a system that can treat around 80 L of Chromium (VI) contaminated water. This treatment system with E. crassipes biomass and EDTA with proportions of 9:1 costs around USD 10, which is quite cheap compared to conventional ones.

Recent Advances in the Treatment of Industrial Wastewater from Different Celluloses in Continuous Systems

There are numerous studies on water care methods featured in various academic and research journals around the world. One research area is cellulose residue coupled with continuous systems to identify which are more efficient and easier to install. Investigations have included mathematical design models that provide methods for developing and commissioning industrial wastewater treatment plants, but nothing is provided on how to size and start these treatment systems. Therefore, the objective is to determine recent advances in the treatment of industrial wastewater from different celluloses in continuous systems. The dynamic behavior of the research results with cellulose biomasses was analyzed with the mass balance model and extra-particle and intraparticle dispersion, evaluating adsorption capacities, design variables, and removal constants, and making a size contribution for each cellulose analyzed using adsorption capacities. A mathematical model was also developed that feeds on cellulose reuse, determining new adsorption capacities and concluding that the implementation of cellulose waste treatment systems has a high feasibility due to low costs and high adsorption capacities. Furthermore, with the design equations, the companies themselves could design their systems for the treatment of water contaminated with heavy metals with cellulose.

Maize cob (Zea mays) as natural biomass sorbent for crude oil biosorptive removal from contaminated seawater: Taguchi process optimization and biosorptive removal mechanism

Crude oil pollution poses a serious threat to the aquatic environment. Hence, there is an increasing interest in developing an efficient cleaner process technique for oil spill cleanup via agricultural biomass waste-organic sorbent utilization. This work evaluated the effects of independent biosorptive removal at three varying levels (initial concentration of crude oil (Z1, 7.8-15.6 g/L), seawater-oil temperature (Z2, 25-45 °C), sorbent dose (Z3, 1-3 g), and sorbent particle size diameter (Z4, 1.18-4.72 mm)) on the biosorptive removal efficiency and biosorptive capacity performance of maize cob sorbent for crude oil biosorptive removal from seawater. Experiments were designed based on Taguchi orthogonal array experimental design (L9(34)) to study the effects and process optimization. The results revealed that the maize cob sorbent's crude oil biosorptive removal efficiency is related to Z1, Z3, and Z4, while the biosorptive capacity is related to Z1 and Z3. The optimum biosorptive removal efficiency and the biosorptive capacity values were 96.53% and 12.64 g/g, respectively, achieved at optimum factors of Z1 (7.8 g/L), Z3 (3 g), and Z4 (1.18 mm), as well as at Z1 (15.6 g) and Z3 (1 g). The isotherm and kinetic data, respectively, followed the Langmuir isotherms and the pseudo-second-order kinetics with a maximum monolayer biosorptive capacity of 23.31 g g-1. The mechanism of biosorptive crude oil removal was by physical sorption and film diffusion control. Therefore, the maize cob represents an inexpensive and effective natural sorbent for oil spill removal from water bodies.

Development of a treatment for water contaminated with Cr (VI) using cellulose xanthogenate from E. crassipes on a pilot scale

Water care is an imperative duty in industries with effluents loaded with pollutants such as heavy metals, especially chromium (VI), extremely dangerous for humans and the environment. One way of treating water is possible through a continuous system with dry and crushed vegetable biomass of cellulose xanthogenate because it can adsorb heavy metals, especially due to its low production costs. Through continuous systems and with the waste of PET plastics, it is possible to develop a water treatment process adapting this system and biomass. The objective of this research is the development of a treatment for water contaminated with Cr (VI) using cellulose xanthogenate from E. crassipes on a pilot scale. Where a mass balance conducted to determine the adsorption capacity of this heavy metal, corroborating it through the Thomas model. The treatment process eliminated around 95% of Cr (VI) present in the water, in addition, biomass reuse cycles carried out, which maintained a considerable adsorption capacity in all the cycles conducted through EDTA reagent.

Design of a Fixed-Bed Column with Vegetal Biomass and Its Recycling for Cr (VI) Treatment

The aim of this work is to design a fixed-bed column with vegetal biomass of Eichhornia crassipes and the process of recycling it for treatment via the adsorption of water loaded with chromium (VI). In the first stage, the relationship between the fixed-bed density and the microparticle density is calculated, giving a model for the design of the fixed bed. Using this model, two systems for the treatment of Cr (VI)-contaminated water were designed and built. The vegetable biomass at three particle diameters of 0.212 mm, 0.30 mm and 0.45 mm was evaluated in the removal of Cr (VI) from water using the designed fixed-bed systems, giving the best removal of Cr (VI) with the lowest size particles and allowing the validation of the proposed model with the Thomas model. The incorporation of iron into the biomass allowed for the treatment of near 2.0 L of polluted solution, removing around 90% of Cr (VI), while it was only possible to treat nearly 1.5 L when using raw biomass, removing around 80% of Cr (VI). The recycling of the biomass was achieved via the elution of Cr (VI) with EDTA, permitting the reuse of the material for more than five treatment cycles.

Study of Barium Adsorption from Aqueous Solutions Using Copper Ferrite and Copper Ferrite/rGO Magnetic Adsorbents

The development of advanced materials for the removal of heavy metal ions is a never-ending quest of environmental remediation. In this study, a facile and cost-effective approach was employed to synthesize copper ferrite (CF) and copper ferrite/reduced graphene oxide (CG) by microwave assisted combustion method for potential removal of barium ions from aqueous medium. The physiochemical characterizations indicated the formation of magnetic nanocomposite with an average crystallite size of CF and CG is 32.4 and 30.3 nm and with specific surface area of 0.66 and 5.74 m2/g. The magnetic results possess multidomain microstructures with saturation magnetization of 37.11 and 33.84 emu/g for CF and CG. The adsorption studies prove that upon addition of rGO on the spherical spinel ferrite, the adsorption performance was greatly improved for CG nanocomposite when compared with the bare CF nanoparticles. The proposed magnetic adsorbent demonstrated a relatively high Ba2+ adsorption capacity of 161.6 mg·g-1 for CG nanocomposite when compared to 86.6 mg·g-1 for CF nanoparticles under optimum conditions ( $\text{pH}=7;T={25}^{°}\text{C}$ ). The pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich models were fitted to the kinetic data, the yielded $R^2$ value of 0.9993 (PSO) for CF and 0.9994 (PSO) for CG which is greater than the other two models, which signify that the adsorption process is chemisorption. Thermodynamic studies show that barium adsorption using CF and CG adsorbents is endothermic. The as-fabricated CuFe2O4/rGO nanocomposite represents a propitious candidate for the removal of heavy metal ions from aqueous solutions.

Modified biochar improves the storage capacity and adsorption affinity of organic phosphorus in soil

The loss of soil organic phosphorus can easily cause water eutrophication. In order to effectively reduce the loss of soil organic phosphorus, this manuscript investigated the adsorption of soil organic phosphorus by lanthanum modified biochar (BC), traditional adsorbent gypsum (GY) and zeolite (ZE) by taking phytic acid as the representative. The adsorption isotherm model and kinetic models were used to fit the phosphorus absorption characteristics of the adsorbents. The effects of initial pH and temperature on the adsorption capacity were discussed, and the adsorption mechanism of each adsorbent was explained by means of FTIR and XRD. The results showed that the adsorption capacity of phytate phosphorus followed the trend of BCTS > GYTS > ZETS > TS (soil), and the maximum phosphorus adsorption capacity obtained from Langmuir isotherm for treatment with BCTS was 2.836 mg g^-1, and the treatment had the strongest affinity for phytate phosphorus and also the ability to store phosphorus. The adsorption process fits well with Langmuir isotherm equation and pseudo-second-order kinetic equation, and the adsorption behavior of phytate phosphorus was mainly controlled by the chemisorption of monolayer. When the concentration of phytate phosphorus was 100 mg L^-1, percentage of modified biochar added to the soil was 3% and the pH was 6, the adsorption capacity reached the maximum, and the maximum adsorption capacity was 2.000 mg g^-1. The results of FTIR and XRD characterization showed that complexation was the main adsorption mechanism. In this study, the combination of modified biochar and soil phytate phosphorus can provide a good theoretical basis for reducing the loss of soil organic phosphorus.

Green synthesis, characterization, application and functionality of nitrogen-doped MgO/graphene nanocomposite

A facile, feasible, and green synthesis via an electrochemical exfoliation process was applied to synthesize nitrogen-doped MgO/graphene nanocomposite (N-MgO/G). The N-MgO/G nanocomposite was characterized by several analytical techniques including X-ray photoelectron spectroscopy, X-ray powder diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction, and elemental mapping analysis. N-MgO/G nanocomposite was then applied to adsorb lead metal ions (Pb²⁺) from aqueous solutions. The N-MgO/G nanocomposite demonstrated a remarkably high Langmuir maximum adsorption capacity (294.12 mg/g) for Pb²⁺ ions under the optimum experimental conditions at a pH of 5.13, time of 35 min, dose of 0.025 g, the concentration of 400 mg/L, and a temperature of 36 °C. Adsorption kinetics results fitted with a pseudo-second-order model and a thermodynamic study showed that Pb²⁺ adsorption is an endothermic process. The practical application of N-MgO/G was also investigated to test its applicability in real water samples collected from different sources such as deionized water, tap water, wastewater, and river water.

Chromium Contamination from Tanning Industries and Phytoremediation Potential of Native Plants: A Study of Savar Tannery Industrial Estate in Dhaka, Bangladesh

Tannery wastewater is a significant cause of chromium (Cr) contamination in land and water. This study assessed Cr contamination caused by the discharge of tannery wastewater in the Dhaleshwari River and identified possible native plants for phytoremediation of Cr. Water, soil and sediments samples were collected from upstream and downstream of the wastewater discharge channel of Savar tannery industrial estate situated on the bank of the river. Samples of root, stem, leaf and fruit of four selected plants (i.e., Eichhornia crassipes, Xanthium strumarium L., Cynodon dactylon, Croton bonplandianum Baill.) were also collected from those sampling points. The total Cr in acid digested samples were determined by flame atomic absorption spectrometry. High concentrations of Cr were detected in the water, soil and sediment samples collected near the wastewater discharge channel. Of all the plant species, Xanthium strumarium L. exhibited high translocation factors (TF) and bioconcentration factors (BCF) for Cr. Based on the findings of this study Xanthium strumarium L. is preferable as a native species for phytoremediation of Cr.

Adsorptive removal of Rhodamine B dye from aqueous solution by using graphene-based nickel nanocomposite

In this work, reduced graphene oxide-nickel (RGO–Ni) nanocomposite is synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM–EDS (Energy Dispersive X-Ray Spectroscopy) are used to study the crystalline nature, morphology and elemental composition of the RGO–Ni nanocomposite, respectively. As synthesized RGO–Ni nanocomposite is used to develop selective adsorptive removal of Rhodamine B (RhB) dye from the aqueous solution. The experiments have been performed to investigate RhB uptake via RGO–Ni nanocomposites which include, contact time (60 min), initial dye concentration (50 mg/100 ml), adsorbent dosage (0.5 mg) and pH 8 of dye solution. The equilibrium concentration is determined by using different models namely, Freundlich, Langmuir and Tempkin. Langmuir isotherm has been fitted well. Langmuir and Tempkin equations are determined to have good agreement with the correlation coefficient data. The kinetic study concluded that RhB dye adsorption follows with the pseudo-second-order kinetic model. Further, adsorption mechanism of RGO–Ni is proposed which involves three steps. The synthesized adsorbent is compared with the other adsorbents in the literature and indicates that RGO–Ni nanocomposite used in this study shown better results for a particular adsorption capacity than polymeric, natural and synthetic bioadsorbents. The regeneration and reusability experiments suggest RGO–Ni nanocomposite can be used for many numbers of times for purification/adsorption.

Employing waste to manage waste: Utilizing waste biomaterials for the elimination of hazardous contaminant [Cr(VI)] from aqueous matrices

Pollution caused due to discharge of toxic and hazardous chemical contaminants from industrial processes is an issue of major environmental concern. Hexavalent chromium [Cr(VI)] is one such known toxic heavy metal contaminant emanated largely from various industrial processes. Since physical-chemical treatment techniques are beset with several problems, there is an increased attention on the use of waste biomaterials/biomass as sorbents for the elimination of heavy metals from aqueous matrices. The main purpose of this study was to evaluate the effectiveness of some low-cost waste biomaterials such as fruit wastes, agricultural and industrial waste/byproducts, waste parts of photosynthetic plants, aquatic plants and fungal biomass collected from different sources for the biosorption of Cr(VI) from aqueous matrices. Amid the tested biomaterials, wood apple shell (WAS) biomass (Limonia acidissima) was found to be highly efficient biosorbent for Cr(VI) sorption. In majority of biomass, it was observed that biosorption of Cr(VI) took place at acidic pH with optimum pH ranging from 2.0 to 5.0. Loading capacity of WAS biomass (29.37 mg/g) was higher than that of conventional adsorbent activated charcoal (26.56 mg/g), which was used as control. Cr(VI) treated biomass (WAS) was characterized using instrumental techniques such as Scanned Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) confirmed the adsorption of Cr(VI). Boehm titration and FTIR studies were conducted to ascertain the presence of functional groups responsible for Cr(VI) sorption by WAS biomass. The WAS biomass removed Cr(VI) from industrial wastewater with an efficiency of >99.9% thus complying with the statutory limits. Considering the economical aspect, the selected biomass can be viewed as a potential candidate for the elimination of toxic contaminant from wastewater.

Design and development of a biotreatment of E. crassipes for the decontamination of water with Chromium (VI)

The use of cellulose materials for the adsorption of heavy metals has increased in favorable results to comply with the removal of these contaminants from water, such as the case of Chromium (VI), being one of the most dangerous heavy metals for the environment and human health. The objective of this research is to design and develop a biotreatment with dry and crushed biomass of E. crassipes for the continuous treatment of Chromium (VI), determining through mathematical modeling the Fick diffusion constant (Kf), based on this constant Fick will establish the performance of the biotreatment and the intraparticle diffusion constant (Ks). The diffusion speed (Kf) of the biomass of E. crassipes chemisorbing Cr (VI) of 0.30 cm/min, also it got the constant of the adsorption capacities (Ks) was 0.0198 s. With (Kf) it can design the treatment systems according to caudal or load greatly contaminated, calibrating the parameters how caudal, volume, or area of contact of the system of treatment. Also with (Ks) will be possible the design and modeling of a treatment system to improve the capacity of adsorptions calibrating the density of the particle and the density of the contact bed of the treatment system. Based on Fick's second law, an equation was designed to determine the reliability and performance of water treatment systems through the E. crassipes plant.

Design and development of a biotreatment of E. crassipes for the decontamination of water with Chromium (VI)

The use of cellulose materials for the adsorption of heavy metals has increased in favorable results to comply with the removal of these contaminants from water, such as the case of Chromium (VI), being one of the most dangerous heavy metals for the environment and human health. The objective of this research is to design and develop a biotreatment with dry and crushed biomass of E. crassipes for the continuous treatment of Chromium (VI), determining through mathematical modeling the Fick diffusion constant (Kf), based on this constant Fick will establish the performance of the biotreatment and the intraparticle diffusion constant (Ks). The diffusion speed (Kf) of the biomass of E. crassipes chemisorbing Cr (VI) of 0.30 cm/min, also it got the constant of the adsorption capacities (Ks) was 0.0198 s. With (Kf) it can design the treatment systems according to caudal or load greatly contaminated, calibrating the parameters how caudal, volume, or area of contact of the system of treatment. Also with (Ks) will be possible the design and modeling of a treatment system to improve the capacity of adsorptions calibrating the density of the particle and the density of the contact bed of the treatment system. Based on Fick's second law, an equation was designed to determine the reliability and performance of water treatment systems through the E. crassipes plant.

A meta-analysis of metal biosorption by suspended bacteria from three phyla

Biosorption of heavy metals by bacterial biomass has been the subject of significant research interest in last decades due to its efficiency, relatively low cost and minimal negative effects for the surrounding environment. In this meta-analysis, the biosorption efficiencies of different bacterial strains for Cu(II), Cd(II), Zn(II), Cr(III), Mn(II), Pb(II) and Ni(II) were evaluated. Optimum conditions for the biosorption process such as initial metal concentration, temperature, pH, contact time, metal type, biomass dosage and bacterial phyla, were evaluated for each heavy metal. According to the results, the efficiencies of bacterial biomass for removal of heavy metal were as follows: Cd(II) > Cr(III) > Pb(II) > Zn(II) > Cu(II) > Ni(II) > Mn(II). Firmicute phyla showed the highest overall (living and dead) biosorption efficiency for heavy metals. Living biomass of Proteobacteria had the best biosorption performance. Living bacterial biomass was significantly more efficient in biosorption of Cu(II), Zn(II) and Pb(II) than dead biomass. The maximum biosorption efficiency of bacterial strains for Cd(II), Pb(II) and Zn(II) was achieved at pH values between 6 and 7.5. High temperatures (>35 °C) reduced the removal efficiencies for Cu(II) and Zn(II) and increased the efficiencies for Cd(II) and Cr(III) ions. The maximum biosorption efficiency of non-essential heavy metals occurred with short contact times (<2 h). Essential metals such as Zn and Cu were more efficiently removed with long biosorption durations (>24 h). The mean biosorption capacity of bacterial biomass was between 71.26 and 125.88 mg g^-1. No publication bias existed according to Egger's and Begg's test results.

Adsorption of lead ions from wastewater using nano silica spheres synthesized on calcium carbonate templates

Lead is a heavy metal that is bio accumulative and non-biodegradable that poses a threat to our health when it exists in excess in our bloodstream. It has found its way into wastewater from mostly chemical industrial processes. In this article, we investigated the adsorption and hence removal of lead (II) ions from wastewater in order to purify it for re-use in industrial processes or for plant and animal use. We synthesized nano silica hollow spheres (NSHS) and used them as adsorbents to remove lead ions from wastewater. When we characterized the NSHS using X-Ray diffraction, the amorphous nature of silica was evident with average crystal size of 39.5 nm. Scanning electron microscopy was used to determine the morphology of the adsorbent and the particles were found to be spherical in shape within a size range of 100–200 nm. Thermogravimetric analysis was used to determine the mass loss of NSHS which was ~2% at 800 °C. Our experimental results from adsorption studies showed that there was a linear relationship between temperature (27–60 °C) and adsorption efficiency and an inverse relationship between initial metal concentration (50–300 mg/L) and adsorption efficiency. At a maximum temperature of 60 °C and maximum initial metal concentration of 300 mg/L, the adsorption capacity was 200 mg/g and 262 mg/g, respectively while the adsorption efficiency was 99.6% and 87.4%, respectively. Our equilibrium and thermodynamic results revealed that the process was better modelled by the Langmuir adsorption isotherm (q_max = 266.89 mg/g and b = 0.89 L/mg). The adsorption process was both endothermic (ΔH = 97 kJ/mol) and spontaneous (ΔG = -22 kJ/mol). We can conclude that we were able to successfully synthesize NSHS, use them to remove lead (II) ions and the produced NSHS have a capacity that is higher than most other adsorbents investigated by other researchers.

Advances in application of cotton-based adsorbents for heavy metals trapping, surface modifications and future perspectives

Cotton-based adsorbents (CBAs) are promising materials for combating the problem of heavy metal pollution of environmental waters. This is ascribed to the low cost, abundance, biodegradability and efficiency of CBAs. Herein we review the adsorption of heavy metals (HMs) onto CBAs. We found that several surface modifications were employed to improve the efficiency of the CBAs. These modifications were effected via thermal, physical and chemical means to obtain activated carbons, biochars, ionic liquids, aerogels, hydrogels, chitosans and nanoparticle-derived CBAs. The CBAs exhibited maximum HMs uptake as low as 0.002 mg/g to as high as 505.6 mg/g. Although, the cotton-derived activated carbons and biochars exhibited enhanced HM uptake from that of the unmodified CBAs, they were less efficient than CBAs modified by other methods. Recent chemical, ionic liquid, chitosan and nano-derived CBAs were the most efficient, with high uptake and fast kinetic removal. However, the nanoparticle-based adsorbents are preferred to the chemically modified forms, due to the possibility of secondary pollution and the noxious effect of the latter to the environment. Findings showed that chemical treatment produced CBAs most efficient for As(V), Pb(II) and Fe(III), while ionic liquid CBA was more efficient for Cu(II) and Ni(II). Nano-based treatment was suitable for the uptake of Co(II), Zn(II), Pb(II) and Cd(II), while the chitosan based adsorbent was viable for Hg(II). Isotherm and kinetic evaluation of CBAs mostly conformed to the Langmuir and pseudo-second order models, respectively. Spontaneous adsorption of HMs onto CBAs was deduced from thermodynamic analysis, with endothermic and exothermic characteristics. Over 88% desorption of HMs was obtained from the CBAs studied with good average reusability from 3 to 20 cycles. We also discussed the directions for future research.