Adsorption

The Earth's surface is covered by 75% water. However, only 3% of this water is freshwater, and just 1% of that freshwater is accessible for human consumption. In most instances, humans are responsible for introducing pollutants into water. Dyes are among the most significant pollutants found in textile wastewater. As a result of its economic feasibility and high selectivity, adsorption has gained widespread popularity as a technique for treating organic dyes. In this research, a novel magnetic adsorbent was developed and utilized to remove certain toxic dyes.

In this research, Gum Arabic has been utilized as a natural and biodegradable polymer for the preparation of an effective adsorbent. To enhance the surface area, efficiency and stability of this natural polymeric adsorbent, citric acid has been employed as a green crosslinker. According to our findings, ,Gum Arabic has been polymerized for the first time with citric acid as a crosslinker and utilized for the removal of cationic dyes. Additionally, a crosslinked Gum Arabic polymer synthesized using citric acid has been incorporated with magnetite nanoparticles, ensuring its facile recovery from the medium upon application of a magnetic field. Furthermore, the prepared magnetic Gum Arabic was employed for the removal of Crystal Violet (CV), Malachite Green (MG), and Methylene Blue (MB) dyes from aqueous samples.

In this study, the impact of various parameters, including initial dye solution concentration, solution pH, contact time between the adsorbent and the dye solution, adsorbent dosage, and dye solution temperature, on the removal efficiency of   cationic dyes from aqueous samples was investigated. According to the results, the adsorption capacity of the adsorbent (CL-GA/Fe3O4) increased with increasing dye solution concentration, reaching maximum levels of 209.80, 205.12, and 177.12 mg/g for MB, CV, and MG, respectively. Additionally, the removal efficiency for these dyes increased with increasing solution pH, reaching 99.43% (MB), 97.13% (MG), and 96.62% (CV) at a pH of 6. Furthermore, the removal efficiency of dyes increased with increasing adsorption temperature, indicating an endothermic process. It is noteworthy that in this study, both MB and MG dyes reached their maximum removal efficiency after 20 min. In contrast, CV reached its maximum removal efficiency within a 15-min time frame. In this investigation, the Langmuir model showed a significantly better fit to the adsorption data compared to the Freundlich model, indicating its accuracy in describing monolayer adsorption. Additionally, this study revealed that the obtained adsorption kinetic data fit well with the pseudo-second-order model. This suggests that chemisorption likely plays a significant role in the rate-limiting step of the adsorption process.

In this research, a novel nano adsorbent (CL-GA/Fe3O4) based on crosslinked Gum Arabic with citric acid and magnetized with Fe3O4 nanoparticles was employed for the removal of cationic dyes. To validate the effectiveness of the (CL-GA/Fe3O4) adsorbent, various characterization techniques, including FT-IR, FESEM, EDX, Zeta potential, and VSM, were employed. The findings of this study demonstrate the development of an innovative and efficient adsorbent for dye removal, which holds significant importance in addressing environmental challenges.

In this paper, the preparation of nano zeolite was carried out at different grinding times using a dry planetary ball mill. Sodium Hexa Meta Phosphate (SHMP) was introduced as the dispersant in the milling of natural zeolite adsorbent. In the next step, to remove and adsorb heavy metal ions such as nickel, copper, and cadmium, the application of nano zeolite was studied in batch mode.

In this paper, zeolite nanoparticles were produced using planetary and ball mills. Adsorption experiments were conducted to investigate the adsorption of nickel, copper, and cadmium using new nano zeolite adsorbent. 

The effect of Sodium Hexa Meta Phosphate (SHMP) on grinding and adsorption of ion metals by nano zeolite was investigated and results showed that the application of SHMP led to lower energy consumption in grinding and had a positive effect on nickel and cadmium removal from aqueous solution by nano zeolite particles.

The effect of sodium hexametaphosphate on the absorption of nickel, cadmium, and copper metals showed that this reagent had a positive effect on the absorption of nickel and cadmium ions on nanozeolite particles, but it did not affect the absorption of copper ions. Nano-zeolites have a larger external surface area and a shorter diffusion path length due to having nano-sized particles, so their absorption capacity is very high.

The increase of various industries and the ever-increasing growth of the population of the planet have caused all kinds of contamination in the environment. One of the most important contaminants in water, which has many risks for human health and living organisms and important environmental risks, is anionic compounds in high concentration. Chromium is one of these contaminants that causes contamination in the environment and brings many risks to human health and other living organisms. Various methods have been evaluated to remove heavy metals from water, which often include chemical or energy-intensive processes. Therefore, it is important to modify these sources with the help of affordable adsorbents and with low energy consumption. Previous studies showed that biochar, metal-coated biochars and carbon-metal composites are highly effective in removing chromium contaminants with a concentration of 20 mg/liter from water, but so far the effect of these adsorbents on removing this anionic contaminant in high concentrations has not been investigated.

In this research, the efficiency of different adsorbents (biochar, copper-coated biochar, aluminum-coated biochar, iron-coated biochar, biochar-copper composite, biochar-aluminum composite and biochar-iron composite) on the removal of chromium, with a concentration of 300 mg per liter, from water was investigated. Metal-coated biochars were prepared from the combination of metals (copper, iron and aluminum) with a concentration of 10000 mg/kg with biochar produced at 600 degrees Celsius and various biochar-metal composites were prepared from the combination of these metals with rice straw and then the samples were pyrolyzed at 600 degrees Celsius. In order to determine the efficiency of the adsorbents, 0.5 grams of each adsorbent was mixed with 40 ml of chromium solution with a concentration of 300 mg/l and pH= 6 and shaken for three hours until they reached equilibrium. Then the samples were centrifuged for 5 minutes at 6000 rpm and after the filtration, the final concentration of the contaminant was obtained and the percentage of chromium removal was calculated.

The results of the present study showed that all of the applied adsorbents were effective in removing high concentrations of chromium from water. The lowest removal rate of this contaminant was related to the biochar sample, which only removed 15.28% of this contaminant from water; And the highest amount of removal was achieved using iron composite, which removed 44.45% of the contaminant from the aqueous solution. According to the results of this research, it can be observed that coating biochar and rice straw with metals has been able to increase the efficiency of this adsorbent in removing chromium from water. For example, iron composite and iron-coated biochar were able to remove 44.45 and 30.86% of chromium contaminant from the aqueous solution, respectively, while rice straw biochar was only able to remove 15.28% of this contaminant from water.

The results of present study showed that iron coated biochar and biochar-iron composite had more ability to remove chromium contaminant from aqueous solution than other metal coated biochars and biochar-metal composites and were able to perform more successfully. Therefore, the use of these adsorbents can be effective in the treatment of chromium-contaminated water.

In this study, hydroxyapatite-supported zero-valent iron nanoparticle was synthesized by the sodium borohydride reduction method. To evaluate the performance of adsorbent for the removal of Cu(II) and Ni(II) ions, the influence of different sorption parameters, such as contact time, temperature, initial concentration of metal ions, the dosage of adsorbent, and pH value of the solutions were investigated. The highest removal efficiency of both metals occurred under the optimal conditions of 7, 45 min, 0.1, 50 ºC, and 5 mg/l for pH, contact time, adsorbent mass, temperature, and initial concentration, respectively. The kinetic and equilibrium data were well fitted by the pseudo-second-order model and Langmuir- Freundlich model, respectively. The maximum adsorption capacities of adsorbent towards Cu(II) and Ni(II) were 138 and 108 mg/g, respectively. The results indicated that the adsorbent could remove the majority of metals (95%) within 40 min without pH control. Thermodynamic parameters, i.e., ΔG°, ΔH°, and ΔS°, indicated that the sorption process was spontaneous and thermodynamically favorable.

 Landfill leachate is a highly toxic and hazardous form of wastewater due to its complex composition characteristics. Effective removal of heavy metals from landfill leachate is of great concern due to the fact that toxic metals can seriously threaten the food chain, and therefore the human health. The main objective of this work was to study the utilizing of low-cost pruning residues in the production of biochar and its application in removal of lead (Pb) from landfill leachate.

 Leachate produced in Babol municipal solid waste landfill was used as an adsorbent solution. Pruning residues were collected and used for biochar preparation. Biochar produced under the pyrolytic temperature of 700°C with a 1-hour retention time. The adsorption mechanism of pruning waste biochar to Pb was analyzed through BET surface area and scanning electron microscope (SEM) tests. Batch experiments were performed to study the effects of adsorption parameters on Pb removal. The influence of contact time (30-300 min), adsorbent dosage (1-50 g/L), as well as particle size (1-2 mm and 63-75 µm) was investigated. Moreover, the kinetic and isotherm models were applied to the experimental data to predict the adsorption parameters.

 The results obtained from the analysis of the untreated Babol landfill leachate was revealed that the Pb concentration was about 4.94 mg L-1. The surface area of the produced biochar was determined to be 292.44 m2 g-1. SEM microstructure of the biochar showed the developed surface area with visible pores. All of these data seem to suggest a great potential for pruning residues biochar to Pb removal. The adsorption of Pb was mainly affected by contact time, adsorbent dose, and biochar particle size. Higher contact time and adsorbent dosage showed higher uptake of Pb. Whereas, the uptake of Pb ions onto pruning residues biochar was substantially reduced with increase the biochar particle size. Maximum Pb percentage removal was observed at a contact time of 90 min and with an optimum biochar dosage of 20 g L-1 (89.06% removal) for biochar with 1-2 mm particle size. While, biochar with particle size of 64-75 µm can removed Pb to almost 100% at a contact time of 120 min and with an optimum biochar dosage of 20 g L-1. The kinetic study showed that adsorption can be well described by the pseudo-second order kinetic model. This supports the chemisorption theory behind the pseudo-second order kinetic model for the adsorption system. The results of isotherm models implied that the behaviors of the isotherms are more appropriate for the Langmuir model, showing a monolayer adsorption capacity for Pb.

 Findings of this research demonstrated the applicabil ity of pruning residues biochar as an economic adsorbent for the removal of the Pb from landfill leachate. On the other hand, the crop residue burning poses a threat to the environment and human health due to the emission of toxic gasses and particulate matter. So, conversion of pruning residues to biochar and its application to heavy metal removal is a useful and environment-friendly alternative to crop residue and biomass burning.

The performance of the Fe3O4- CeO2- NH2/ chitosan/ Polyvinyl alcohol nano hybrid synthesized by casting method was investigated for the adsorption of Cu (II) and Ni (II) cations from water system. The synthesized nano hybrid adsorbents were characterized by FESEM, BET and FTIR analyses. The effect of single and binary oxides content, Fe3O4-CeO2-NH2 content, pH, initial cation concentration, contact time and temperature on the adsorption capacity was evaluated in a batch system. The results showed that the adsorption capacity significantly increased after modification of adsorbent with Fe3O4- CeO2- NH2 nanoparticles. The kinetic and equilibrium data were accurately evaluated by the double- exponential and Redlich- Peterson models, respectively. The maximum adsorption capacity of nano hybrid adsorbent was estimated to be 246.9 and 88.6 mg / g at 45 º C for Cu (II) and Ni (II) cations, respectively. Thermodynamic investigation indicated an endothermic and spontaneous adsorption for both metal cations; and adsorption was favored at higher temperature. The synthesized nano hybrid can be easily regenerated after five cycles of adsorption- desorption.