Adsorption of nitrate onto anionic bio-graphene nanosheet from aqueous solutions: Isotherm and kinetic study

Structure properties and industrial applications of anion exchange resins for the removal of electroactive nitrate ions from contaminated water

The presence of nitrates in lakes, rivers, and groundwater is common. Anion exchange resins (AER) are polymeric structures that contain functional groups as well as a variety of particle sizes that are used for removing nitrate ions from solutions. This article provides a concise review of the types and properties of AER, synthesis methods, characterization, and environmental applications of AER. It discusses how different factors affect the adsorption process, isotherm and kinetic parameters, the adsorption mechanism, and the maximum adsorption capacities. Additionally, the present review addresses AER's regeneration and practical stability. It emphasizes the progress and proposes future strategies for addressing nitrate pollution using AER to overcome the challenges. This review aims to act as a reference for researchers working in the advancement of ion exchange resins and presents a clear and concise scientific analysis of the use of AER in nitrate adsorption. It is evident from the literature survey that AER is highly effective at removing nitrate ions from wastewater effluents.

Adsorbent based on MOF-5/cellulose aerogel composite for adsorption of organic dyes from wastewater

Industries persistently contribute to environmental pollution by releasing a multitude of harmful substances, including organic dyes, which represent a significant hazard to human health. As a result, the demand for effective adsorbents in wastewater treatment technology is steadily increasing so as to mitigate or eradicate these environmental risks. In response to this challenge, we have developed an advanced composite known as MOF-5/Cellulose aerogel, utilizing the Pampas plant as a natural material in the production of cellulose aerogel. Our investigation focused on analyzing the adsorption and flexibility characteristics of this novel composite for organic dye removal. Additionally, we conducted tests to assess the aerogel's reusability and determined that its absorption rate remained consistent, with the adsorption capacity of the MOF-5/cellulose aerogel composite only experiencing a marginal 5% reduction. Characterization of the material was conducted through XRD analysis, revealing the cubic structure of MOF aerogel particles under scanning electron microscopy. Our study unequivocally demonstrates the superior adsorption capabilities of the MOF-5/cellulose aerogel composite, particularly evident in its efficient removal of acid blue dye, as evaluated meticulously using UV-Vis spectrophotometric techniques. Notably, our findings revealed an impressive 96% absorption rate for the anionic dye under acidic pH conditions. Furthermore, the synthesized MOF-5/cellulose aerogel composite exhibited Langmuir isotherm behavior and followed pseudo-second-order kinetics during the absorption process. With its remarkable absorption efficiency, MOF-5/cellulose aerogel composites are poised to emerge as leading adsorbents for water purification and various other applications.

Functional graphene oxide for organic pollutants removal from wastewater: a mini review

Graphene oxide (GO), an important derivative of graphene, with a variety of active oxygen-containing groups (hydroxyl, carboxyl and epoxy) on its surface is easy to be functionalized to obtain adsorbent with high adsorption capacity. To date, the adsorption behaviour of organic pollutants by functionalized GO adsorbents have been extensively studied, but there has been no systematic review regarding the functionalization method of GO for the purpose to remove organic pollutants from wastewater. The leading objective of this review is to (i) summarize the functionalization strategies of GO for organic pollutants removal (covalent functionalization and non-covalent functionalization), (ii) evaluate the adsorption performance of functional GO towards organic pollutants by taking aromatic pollutants and dyes as examples and (iii) discuss the regeneration property and adsorption mechanism of functional GO adsorbent. In addition, the problems of existing studies and future research directions are also identified briefly.

4-Chlorophenol adsorption from water solutions by activated carbon functionalized with amine groups: response surface method and artificial neural networks

4-Chlorophenol pollution is a significant environmental concern. In this study, powdered activated carbon modified with amine groups is synthesized and investigated its efficiency in removing 4-chlorophenols from aqueous environments. Response surface methodology (RSM) and central composite design (CCD) were used to investigate the effect of different parameters, including pH, contact time, adsorbent dosage, and initial 4-chlorophenol concentration, on 4-chlorophenol removal efficiency. The RSM-CCD approach was implemented in R software to design and analyze the experiments. The statistical analysis of variance (ANOVA) was used to describe the roles of effecting parameters on response. Isotherm and kinetic studies were done with three Langmuir, Freundlich, and Temkin isotherm models and four pseudo-first-order, pseudo-second-order, Elovich, and intraparticle kinetic models in both linear and non-linear forms. The synthesized adsorbent was characterized using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses. The results showed that the synthesized modified activated carbon had a maximum adsorption capacity of 316.1 mg/g and exhibited high efficiency in removing 4-chlorophenols. The optimal conditions for the highest removal efficiency were an adsorbent dosage of 0.55 g/L, contact time of 35 min, initial concentration of 4-chlorophenol of 110 mg/L, and pH of 3. The thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The synthesized adsorbent also showed excellent reusability even after five successive cycles. These findings demonstrate the potential of modified activated carbon as an effective method for removing 4-chlorophenols from aqueous environments and contributing to developing sustainable and efficient water treatment technologies.

Combination of advanced nano-Fenton process and sonication for destruction of diclofenac and variables optimization using response surface method

Diclofenac (DCF) as a non-steroidal pharmaceutical has been detected in aquatic samples more than other compounds due to its high consumption and limited biodegradability. In this study, ultrasound waves were applied along with an advanced nano-Fenton process (US/ANF) to remove DCF, and subsequently, the synergistic effect was determined. Before that, the efficiency of the US and ANF processes was separately studied. The central composite design was used as one of the most applicable responses surface method techniques to determine the main and interactive effect of the factors influencing DCF removal efficiency in US/ANF. The mean DCF removal efficiency under different operational conditions and at the time of 1-10 min was obtained to be about 4%, 83%, and 95% for the US, ANF, and US/ANF, respectively. Quadratic regression equations for two frequencies of US were developed using multiple regression analysis involving main, quadratic, and interaction effects. The optimum condition for DCF removal was obtained at time of 8.17 min, H/F of 10.5 and DCF concentration of 10.12 at 130 kHz US frequency. The synergy index values showed a slight synergistic effect for US/ANF (1.1). Although the synergistic effect of US/ANF is not very remarkable, it can be considered as a quick and efficient process for the removal of DCF from wastewater with a significant amount of mineralization.

Comparative removal of hazardous cationic dyes by MOF-5 and modified graphene oxide

Among cationic dyes, malachite green (MG) is commonly used for dying purposes and also as an inhibitor in aquaculture, food, health, and chemical industries due to its cytotoxic effects. Therefore, MG removal is essential to keep the ecosystem and human health safety. Adsorption is a viable and versatile option and exploring efficient adsorbents have high priority. Herein, MOF-5 and aminated corn Stover reduced graphene oxide (ACS-RGO) of typical adsorbents of metal-organic-frameworks (MOFs) and carbon-based classes were studied for MG removal. MOF-5 and ACS-RGO had a specific surface area and total pore volume of 507.4 and 389.0 m2/g, and 0.271 cm3/g and 0.273 cm3/g, respectively. ACS-RGO was superior for MG adsorption and the kinetic rate coefficient for ACS-RGO was ~ 7.2 times compared to MOF-5. For ACS-RGO, MG removal remained high (> 94%) in a wide range of pH. However, dye removal was pH-dependent for MOF-5 and increased from ~ 32% to ~ 67% by increasing pH from 4 to 12. Increasing dye concentration from 25 mg/L to 100 mg/L decreased adsorption by MOF-5 and ACS-RGO for ~ 30% and 7%, respectively. Dye removal was evident in a few tens of seconds after adding ACS-RGO at doses above 0.5 g/L. A significant loss of 46% in adsorption was observed by decreasing MOF-5 mass from 1 to 0.1 g/L. ACS-RGO removed MG in multilayer with an exceptional adsorption capacity of 1088.27 mg/g. In conclusion, ACS-RGO, and MOF-5 showed promising kinetic rates and adsorption capacities toward MG.

Nitrate and Dissolved Organic Carbon Release in Sandy Soils at Different Liquid/Solid Ratios Amended with Graphene and Classical Soil Improvers

This study emphasizes the importance of employing parallel batch tests with different liquid/solid (L/S) ratios to assess their dissolution mechanisms. Changes in physicochemical parameters (electrical conductivity, pH, and oxidation-reduction potential), as well as the sorption/desorption of dissolved organic carbon (DOC) and nitrate (NO3−) due to graphene addition in a calcareous sandy soil (CS) and in a siliciclastic riverine sandy soil (SS) were assessed via batch experiments at different L/S ratios. Graphene’s production is growing at a great pace, so it’s important to test methods to reuse graphene wastes. The results of soil batch experiments mixed with graphene were compared with classical soil improvers (compost, biochar, and zeolites). The batches were performed using the saturation soil extraction method with deionized water as a proxy of rainwater. The contact time was 48 h. At the end of the experiment, water samples were collected to be analyzed for NO3−, DOC, DIC, Ca, and Mg. Graphene did not alter the physiochemical parameters of both soils. Moreover, its addition did not trigger any NO3− increase respect to control and to other improvers. Biochar increased EC and pH beyond recommended limits for most crops’ growth in both soils. As expected, compost addition produced the highest NO3− release.

Nitrates in the environment: A critical review of their distribution, sensing techniques, ecological effects and remediation

Nitrate pollution is eminent in almost all the developing nations as a result of increased natural activities apart from anthropogenic pollution. The release of nitrates in more than critical quantities into the water bodies causes accretion impacts on living creatures, environmental receptors, and human vigour by accumulation through the food chain. Nitrates have recently acquired researchers' huge attention and extend their roots in environmental contamination of surface and groundwater systems. The presence of nitrate in high concentrations in surface and groundwater triggers several health problems, for instance, methemoglobinemia, diabetes, eruption of infectious disorders, harmfully influence aquatic organisms. Sensing nitrate is an alternate option for monitoring the distribution of nitrate in different water bodies. Here we review electrochemical, spectroscopic, and electrical modes of nitrate sensing. It is concluded that, among the various sensors discussed in this review, FET sensors are the most desirable choice. Their sensitivity, ease of use and scope for miniaturisation are exceptional. Advanced functional materials need to be designed to satiate the growing need for environmental monitoring. Different sources of nitrate contamination in ground and surface water can be estimated using different techniques such as nitrate isotopic composition, co contaminants, water tracers, and other specialized techniques. This review intends to explore the research work on remediation of nitrate from wastewater and soil using different processes such as reverse osmosis, chemical denitrification, biological denitrification, ion exchange, electrodialysis, and adsorption. Denitrification proves as a promising alternative over previously reported techniques in terms of their nitrate removal because of its high cost-effectiveness.

Enhanced adsorption and reduction performance of nitrate by Fe-Pd-Fe3O4 embedded multi-walled carbon nanotubes

Multi walled carbon nanotubes (MWCNTs) have attracted more and more attention as adsorbents due to their excellent adsorption properties. By loading metal particles on MWCNTs, the chemical reduction ability of adsorbed pollutants could be provided, so as to achieve the purpose of adsorption and degradation of pollutants. Therefore, the removal process of NO₃^--N by Fe-Pd-Fe₃O₄/MWCNTs was studied, including rapid adsorption of initial pollutants, gradual reduction of intermediate products and re-adsorption of final products. The results showed that Fe-Pd-Fe₃O₄/MWCNTs completely removed NO₃^--N within 2 h, 39% and 25% of which were converted into NO₂^--N and NH₄⁺-N. The adsorption efficiency, kinetics, capacity and adsorption energy all followed the order of NH₄⁺-N > NO₂^--N > NO₃^--N. With the recoverability and reusability of Fe-Pd-Fe₃O₄/MWCNTs having been confirmed in 5 consecutive cycles, the removal rate of NO₃^--N still reached 43%. It has been shown that MWCNTs prolonged the reducing power for NO₃^--N, due to avoiding the aggregation of metal particles. The rapid adsorption of initial pollutants, effective stepwise reduction and convenient recovery processes were of great value for the rehabilitation of polluted water.

Defluoridationof drinking water by metal impregnated multi-layer green graphene fabricated from trees pruning waste

A novel adsorbent with excellent adsorptive properties for fluoride was prepared through a green and cheap synthesis route. Populus caspica pruning wastes, a cheap agri-waste material, were reduced to multi-layer green graphene (MLG) and then post-modified to aluminum/iron modified multi-layer green graphene (AMLG and IMLG). Batch experiments revealed the effect of pH (3-11), contact time (0.5-12 h), and initial fluoride concentration (5-40 mg/L). The conversion of raw material to MLG increased the specific surface area about 120 times (from 4 to 475 m²/g). Furthermore, a significant improvement in zero points of charge (pHzpc) was attained for IMLG (7.1) and AMLG (8) compared with pristine MLG (4.3). Fluoride showed superior affinity to AMLG and IMLG compared with MLG. Fluoride removal increased gradually by pH from 3 to 8 and then decreased sharply up to pH 11. The study of process dynamics demonstrated the monolayer fluoride adsorption onto AMLG and IMLG controlled by the chemisorptions. The highest predicted adsorption capacities based on the Langmuir model were 31.52, 47.01, and 53.76 mg/g for MLG, IMLG, and AMLG, respectively. Considering economic and technical feasibility presents AMLG and IMLG as a promising candidate against water contamination by elevated fluoride. Graphical abstract.

Modified wheat straw-derived graphene for the removal of Eriochrome Black T: characterization, isotherm, and kinetic studies

A cost-effective and environment-benign adsorbent was prepared from an abundant agro-waste material. Wheat straw was reduced to graphene and then modified by crosslinking to epichlorohydrin. During the conversion process of wheat straw to graphene, the specific surface area increased more than 100 times (from 4 to 415 m² g^-1). The adsorption efficiency of raw wheat straw, graphene nanosheets, and modified graphene against Eriochrome Black T (EBT) were 8.0, 34.7, and 74.4%, respectively. The modified graphene was further investigated for the effect of environmental condition, i.e., pH (3 to 11), EBT concentration (25-100 mg L^-1), adsorbent dosage (0.25-0.75 g L^-1), contact time (5-60 min), and solution temperature (30-60 °C). The dye removal remained at a high level under a wide range of pH from 3 to 9. The EBT removal decreased from 87.3 to 54.5 by increasing dye concentration and increased from 38.2 to 85.4% by increasing adsorbent dose in the studied ranges. Dye removal also increased by mixing time from 5 to 30 min, whereas a slight drop was observed by continuing agitation up to 60 min. Conducting experiments at various temperatures revealed an endothermic process. Pseudo-first-order and pseudo-second-order models were adequate to represent the adsorption kinetics. Isotherm models suggest a multilayer adsorption of EBT molecules on heterogeneous modified graphene surface with a maximum adsorption capacity of 146.2 mg g^-1. The present work demonstrated that the modified graphene obtained from available and low-cost agro-wastes could be used effectively as adsorbent against EBT from aqueous media.

Modeling of chromium (VI) removal from aqueous solution using modified green-Graphene: RSM-CCD approach, optimization, isotherm, and kinetic studies

BACKGROUND

The aim of this study was to investigate the removal of Cr (VI) using Green-Graphene Nanosheets (GGN) synthesized from rice straw.

METHODS

Synthesis of the GGN was optimized using response surface methodology and central composite design (CCD). The effect of two independent variables including KOH-to-raw rice ash (KOH/RRA) ratio and temperature on the specific surface area of the GGN was determined. To have better removal of Cr (VI), GGN was modified using the grafting amine group method. In the Cr (VI) removal process, the effects of four independent variables including initial Cr (VI) concentration, adsorbent dosage, contact time, and initial solution pH were studied.

RESULTS

The results of this study showed that the optimum values of the KOH/RRA ratio and temperature for the preparation of GGN were 10.85 and 749.61 °C, respectively. The maximum amount of SSA obtained at optimum conditions for GGN was 551.14 ± 3.83 m 2 /g. The optimum conditions for Cr (VI) removal were 48.35 mg/L, 1.46 g/L, 44.30 min, and 6.87 for Cr (VI) concentration, adsorbent dosage, contact time, and pH, respectively. Based on variance analysis, the adsorbent dose was the most sensitive factor for Cr (VI) removal. Langmuir isotherm (R2 = 0.991) and Pseudo-second-order kinetic models (R2 = 0.999) were the best fit for the study results and the Q max was 138.89 mg/g.

CONCLUSIONS

It can be concluded that the predicted conditions from the GGN synthesis model and the optimum conditions from the Cr (VI) removal model both agreed with the experimental findings.

Biodegradable chitosan-ethylene glycol hydrogel effectively adsorbs nitrate in water

Nitrate, existing as inorganic anions in water, possesses high water-solubility and has caused lots of contaminations around the world. It is thus extremely urgent to develop an effective method to effectively remove nitrate from water in a sustainable way. In this study, chitosan-ethylene glycol hydrogel (CEGH) was synthesized using the repeated freezing-thawing procedure. A range of batch sorption experiments were conducted to evaluate CEGH as a nitrate sorbent. The adsorption isotherms of nitrate onto CEGH followed the Langmuir model with coefficient of determination of 0.98 and a maximum Langmuir adsorption capacity of 49.04 mg/g, which is higher than that of other adsorbents. The adsorption of nitrate onto CEGH was affected by pH value and temperature. The results indicate that the main removal mechanism was polarity of CEGH molecules given by functional group O-H and N-H and hydrogen bond interaction between CEGH and nitrate molecules under acidic conditions. Therefore, CEGH, a biodegradable carbon-rich adsorbent, can be widely applied to remove nitrate in wastewater treatment and water body remediation.

Valorization of biomass into amine- functionalized bio graphene for efficient ciprofloxacin adsorption in water-modeling and optimization study

A green synthesis approach was conducted to prepare amine-functionalized bio-graphene (AFBG) as an efficient and low cost adsorbent that can be obtained from agricultural wastes. In this study, bio-graphene was successfully used to remove Ciprofloxacin (CIP) from synthetic solutions. The efficacy of adsorbent as a function of operating variables (i.e. pH, time, AFBG dose and CIP concentration) was described by a polynomial model. A optimal99.3% experimental removal was achieved by adjusting the mixing time, AFBG dose, pH and CIP concentration to 58.16, 0.99, 7.47, and 52.9, respectively. Kinetic model revealed that CIP diffusion into the internal layers of AFBG controls the rate of the process. Furthermore, the sorption process was in monolayer with a maximum monolayer capacity of 172.6 mg/g. Adsorption also found to be favored under higher CIP concentrations. The thermodynamic parameters (ΔG°<0, ΔH°>0, and ΔS°>0) demonstrated that the process is endothermic and spontaneous in nature. The regeneration study showed that the AFBG could simply regenerated without significant lost in adsorption capacity.

Enhanced Kinetic Removal of Ciprofloxacin onto Metal-Organic Frameworks by Sonication, Process Optimization and Metal Leaching Study

Metal-organic frameworks (MOFs) are currently recognized as unique platforms for environmental studies. This study evaluated the potential of nine MOFs from ZIF-8, ZIF-67, and UIO-66 families for the removal of ciprofloxacin (CIP), a toxic, bio-accumulative, and persistent fluoroquinolone antibiotic. ZIF-67-SO₄, with a rhombic crystalline morphology and 1375 m²/g BET surface area, has the highest CIP adsorption efficiency among the studied MOFs. The mathematical sorption model predicted that the highest CIP removal (99.2%) occurs when adsorbent dose, pH, and agitation time are adjusted to 6.82, 832.4 mg/L, and 39.95 min, respectively. Further studies revealed that the CIP adsorbed onto ZIF-67-SO₄ in monolayer (q_max: 2537.5 mg/g) and chemisorption controlled the rate of the process. Mass transfer kinetic coefficients improved significantly by sonication at 35 KHz in comparison with mechanical agitation. Thermodynamic parameters (minus signs of ∆G° [7.8 to 14.2], positive signs of ∆H° (58.9 KJ/mol), and ∆S° (0.23 KJ/mol·K)) demonstrated the spontaneous, endothermic, and chemical sorption of CIP. The level of cobalt leached from ZIF-67-SO₄ structure varied 1.2–4.5 mg/L, depending on pH, mixing time, and agitation type. In conclusion, the excellent adsorption properties of ZIF-67-SO₄ for CIP, made it an outstanding candidate for environmental protection purposes.

A lumped-parameter model for investigation of nitrate concentration in drinking water in arid and semi-arid climates and health risk assessment

PURPOSE

This study was conducted to assess the capability of the lumped parameter model (LPM), an efficient model due to its analytical nature and the limited data requirements, to estimate health risks from nitrate in groundwater in arid and semi-arid climates.

METHODS

To assess the capability of LPM, two scenarios were established: one for estimation of hazard quotient (HQ) via monitoring nitrate concentration in groundwater and the other using the LPM. After nitrate was monitored in 148 randomly-selected wells, a modified LPM was used to estimate water volume and nitrate concentration, which ultimately led to the development of a model for estimating HQ. The performances of LPM were assessed using the coefficient of determination, percentage standard deviation, and root mean square error. To compare health risk maps Kriging, Spline, Inverse distance weighted, and natural neighbor models were run using geographical information system (GIS).

RESULTS

Linear analysis revealed a strong correlation between HQ values estimated in LPM and monitoring scenarios in arid climate compared to semi-arid (r = 0.962, n = 22, p = 0.00), suggesting that the LPM was more accurate in predicting nitrate concentration in the arid climate. Uncertainty analysis showed that LPM outputs were sensitive to several parameters, especially leakage from cesspits, which are involved in the sources and sinks of nitrate in the groundwater. In addition, it was found that the natural neighbor was the most appropriate model with the lowest errors for preparing health risk maps from nitrate.

CONCLUSIONS

The obtained results revealed that LPM can be effectively used to estimate nitrate concentration in groundwater in arid climates and thereby LPM is an appropriate model to estimate health risk from nitrate in this climate.

Selective removal of lead ions from aqueous solutions using 1,8-dihydroxyanthraquinone (DHAQ) functionalized graphene oxide; isotherm, kinetic and thermodynamic studies

An anthraquinone - graphene structure was fabricated and applied for the removal of lead(ii) from aqueous solution. The equilibrium occurred in about 10 min revealing the high adsorption rate at the beginning of the process. The maximum Pb(ii) adsorption capacity of the Fe3O4@DHAQ_GO nanocomposite was about 283.5 mg g-1 that was observed at 323 K and pH 5.5. The Pb(ii) adsorption ability increased with the increasing pH. The isotherm and kinetic studies indicated that the Sips isotherm model and the linear form of the pseudo-second kinetic model had a better fit with the experimental results. The positive value of ΔH 0 indicated endothermic interactions between Pb(ii) and Fe3O4@DHAQ_GO. The negative ΔG 0 indicated that the reactions are spontaneous with a high affinity for Pb(ii). The positive ΔS 0 values indicated increasing randomness at the solid-solute interface during the adsorption process. The selective removal of Pb(ii) by the nanocomposite confirms the presence of higher-affinity binding sites for Pb(ii) than Cd(ii), Co(ii), Zn(ii), and Ni(ii) ions. Furthermore, the Fe3O4@DHAQ_GO nanocomposite revealed an excellent preferential adsorbent for Pb(ii) spiked in drinking water samples containing natural ion matrices. EDTA-2NA 0.01 N was found to be a better elution agent than HCl 0.1 M for the nanocomposite regeneration. After five adsorption/desorption cycles using EDTA-2NA 0.01 N, more than 84% of the adsorbed Pb(ii) was still desorbed in 30 min. Capturing sub-ppm initial concentrations of Pb(ii) and the capability to selectively remove lead from drinking water samples make the Fe3O4@DHAQ_GO nanocomposite practically convenient for water treatment purposes. High adsorption capacity and facile chemical synthesis route are the other advancements.