Adsorption of synthetic dyed wastewater using activated carbon from rice husk

Prediction and optimizing of methylene blue sequestration to activated charcoal/magnetic nanocomposites using artificial neutral network and response surface methodology

Green synthesized magnetic nanoparticles (MNPs) linked with activated charcoal (AC) (AC/Fe3O4 NCs) were exploited for methylene blue (MB) confiscation in this study. The AC/Fe3O4 NCs produced were characterized using TEM, FTIR, UV/Vis and XRD spectrometry. The Response-Surface-Methodology (RSM) was utilized to improve the experimental data for the MB sorption to AC/Fe3O4 NCs, with 20 experimental runs implemented through a central composite design (CCD) to assess the effect of sorption factors-initial MB concentration, pH and sorbent dosage effects on the response (removal-effectiveness). The quadratic model was discovered to ideally describe the sorption process, with an R2 value of 0.9857. The theoretical prediction of the experimental data using the Artificial-Neural-Network (ANN) model showed that the Levenberg-Marquardt (LM) had a better performance criterion. Comparison between the modelled experimental and predicted data showed also that the LM algorithm had a high R2 of 0.9922, which showed NN model applicability for defining the sorption of MB to AC/Fe3O4 NCs with practical precision. The results of the non-linear fitting (NLF) of both isotherm and kinetic models, showed that the sorption of MB to AC/Fe3O4 NCs was perfectly described using the pseudo-second-order (PSOM) and Freundlich (FRHM) models. The estimated optimum sorption capacity was 455 mg g-1. Thermodynamically, the sorption of MB to AC/Fe3O4 NCs was shown to be non-spontaneous and endothermic.

Experimental and DFT insights into the adsorption mechanism of methylene blue by alkali-modified corn straw biochar

As an efficient and cost-effective adsorbent, biochar has been widely used in the adsorption and removal of dyes. In this study, a simple NaOH-modified biochar with the pyrolysis temperature of 300 °C (NaCBC300) was synthesized, characterized, and investigated for the adsorption performances and mechanisms of methylene blue (MB). NaCBC300 exhibited excellent MB adsorption performance with maximum removal efficiency and adsorption capacity of 99.98% and 290.71 mg g-1, which were three and four times higher than biochar without modification, respectively. This might be attributed to the increased content of -OH and the formation of irregular flakes after NaOH modification. The Freundlich isotherm suggested multilayer adsorption between NaCBC300 and MB. Spectroscopic characterizations demonstrated that multiple mechanisms including π-π interaction, H-bonding, and pore-filling were involved in the adsorption. According to density functional theory (DFT) calculations, electrostatic interaction between NaCBC300 and MB was verified. The highest possibility of the attraction between NaCBC300 and MB was between -COOH in NaCBC300 and R-N(CH3)2 in MB. This work improved our understanding of the mechanism for MB adsorption by modified biochar and provided practical and theoretical guidance for adsorbent preparation with high adsorption ability for dyes.

Improving adsorption performance of L-ascorbic acid from aqueous solution using magnetic rice husk as an adsorbent: experimental and RSM modeling

In this research, rice husk (RH) was utilized to prepare a magnetic adsorbent for adsorption of ascorbic acid (AA). The magnetic agent is iron(III) chloride (FeCl₃). The impact of acid concentration in the range of 400-800 ppm, adsorbent dosage in the range of 0.5-1 g, and contact time in the range of 10-130 min were studied. The Langmuir model had the highest R² of 0.9982, 0.9996, and 0.9985 at the temperature of 15, 25, and 35 °C, respectively, and the q_max values in these temperatures have been calculated at 19.157, 31.34, and 38.75 mg/g, respectively. The pseudo-second-order kinetic model had the best agreement with the experimental results. In this kinetic model, the values of q have been measured at 36.496, 45.248, and 49.019 mg/g at the acid concentration of 418, 600, and 718 ppm, respectively. The values of ΔH^o and ΔS^o were measured 31.972 kJ/mol and 120.253 kJ/mol K, respectively, which proves the endothermic and irregularity nature of the adsorption of AA. Besides, the optimum conditions of the design-expert software have been obtained 486.929 ppm of acid concentration, 0.875 g of the adsorbent dosage, and 105.397 min of the contact time, and the adsorption efficiency in these conditions was determined at 92.94%. The surface area of the RH and modified RH was determined of 98.17 and 120.23 m²/g, respectively, which confirms the high surface area of these two adsorbents.

A Critical Review of the Removal of Radionuclides from Wastewater Employing Activated Carbon as an Adsorbent

Radionuclide-contaminated water is carcinogenic and poses numerous severe health risks and environmental dangers. The activated carbon (AC)-based adsorption technique has great potential for treating radionuclide-contaminated water due to its simple design, high efficiency, wide pH range, quickness, low cost and environmental friendliness. This critical review first provides a brief overview of the concerned radionuclides with their associated health hazards as well as different removal techniques and their efficacy of removing them. Following this overview, this study summarizes the surface characteristics and adsorption capabilities of AC derived from different biomass precursors. It compares the adsorption performance of AC to other adsorbents, such as zeolite, graphene, carbon nano-tubes and metal-organic frameworks. Furthermore, this study highlights the different factors that influence the physical characteristics of AC and adsorption capacity, including contact time, solution pH, initial concentration of radionuclides, the initial dosage of the adsorbent, and adsorption temperature. The theoretical models of adsorption isotherm and kinetics, along with their fitting parameter values for AC/radionuclide pairs, are also reviewed. Finally, the modification procedures of pristine AC, factors determining AC characteristics and the impact of modifying agents on the adsorption ability of AC are elucidated in this study; therefore, further research and development can be promoted for designing a highly efficient and practical adsorption-based radionuclide removal system.

Chitosan-Modified Biochar and Unmodified Biochar for Methyl Orange: Adsorption Characteristics and Mechanism Exploration

In this study, shrimp shell-derived chitosan (CS) and rice husk-derived biochar (RHB) were produced; CS and RHB were then used to synthesize chitosan-modified biochar (CSBC) hydrogel beads. N₂ adsorption (77K), SEM-EDX and FT-IR techniques were used to evaluate the physicochemical properties of the adsorbents. A batch experiment was conducted to test the methyl orange (MO) adsorption performance of RHB and CSBC. The results showed that the MO adsorption process was strongly pH-dependent. The kinetics were well described by the pseudo-second-order and intra-particle diffusion models, assuming the chemisorption and intraparticle diffusion mechanisms govern the adsorption process. Homogeneous adsorption for MO on the surface of RHB and CSBC was also assumed since the isotherm data showed the best-fit to the Langmuir model. Under the experimental conditions of initial pH 3, dosage 0.2 g, contact time 240 min and temperature 298 K, the maximum adsorption capacity of CSBC and RHB for MO dye adsorption was 38.75 mg.g^-1 and 31.63 mg.g^-1, respectively. This result demonstrated that biochar had better performance after modification with chitosan, which provided more functional groups (i.e., -NH₂ and -OH groups) for enhanced electrostatic interactions and complexation between MO and CSBC. Overall, CSBC is an effective adsorbent for the removal of MO from aqueous solution.

Adsorption of Methylene Blue on Azo Dye Wastewater by Molybdenum Disulfide Nanomaterials

In this study, flower-like MoS2 nanomaterials were synthesized by hydrothermal method with excess thiourea. The adsorption performance of MoS2 adsorbent for methylene blue (MB) in azo dye wastewater was studied. The morphology, crystal phase, and microstructure of nano MoS2 samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The effects of adsorption isotherm, kinetics, different hydrothermal time, and pH on the adsorption experiment were studied. The results showed that the MoS2 adsorbent with a hydrothermal time of 1 h had good adsorption properties for MB. The adsorption data accord with the Langmuir isotherm model, and the maximum adsorption capacity of MoS2 adsorbent is 200 mg/g, and the adsorption kinetics agrees well with the pseudo two-level model. The removal rate of MB is not significantly affected by the pH values. The large pH range can still maintain the removal rate above 93.47%, and the regeneration and recovery properties of MoS2 were also explored. Finally, the adsorption mechanism of MoS2 on MB is discussed.

Simultaneous remediation of polycyclic aromatic hydrocarbon and heavy metals in wastewater with zerovalent iron-titanium oxide nanoparticles (ZVI-TiO2)

The presence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HM) in wastewater is a major challenge to the environment as various approaches have been used to remediate these contaminants from the environment. Zerovalent iron-titanium oxide nanoparticle (ZVI-TiO2 NPs) was synthesized by wet reflux in an inert environment using nitrogen gas and sodium borohydride as reducing agents. Characterization was carried out using a scanning electron microscope (SEM) coupled with electron diffraction X-ray (EDX) and Fourier transform infrared spectrophotometer (FTIR). Assessments of the wastewater were carried out with atomic absorption spectrophotometer (AAS) for HM and a gas chromatography-mass spectrophotometer (GCMS) for PAHs to determine the initial concentration (C i) compared with permissible limits of surface water and adsorption capacity with ZVI-TiO2 NPs (C f), respectively. The results obtained indicate a percentage yield of 65.51 ± 0.01 of ZVI-TiO2 NPs, with a particle size of 100 nm, weight composition of iron, titanium, and oxygen at 49.69, 5.24, and 35.41 g, respectively. FTIR shows a vibrational change of 3465, 2929, and 1641 cm−1 of OH, CH, and CO group needed for metal binding and adsorption. Remediation of HM after acid digestion gave effective removal of zinc, copper, cadmium, cobalt, and lead at an adsorption capacity of 64.29, 54.83, 53.13, 48.39, and 42.66% respectively. The adsorptions of benzo[a]pyrene, fluoranthene, pyrene, benzo[b]fluoranthene, and perylene were 77.87, 67.85, 52.17, 29.50, and 25.45%, respectively. These results indicate that metal/metal oxide (ZVI-TiO2) nanoparticles have a high potential in the remediation of heavy metals and PAHs from the water ecosystem.

A Recent Study on Remediation of Direct Blue 15 Dye Using Halloysite Nanotubes

A set of lab-scale experiments were designed and conducted to remedy Direct Blue 15 (DB15) dye using nontoxic halloysite nanotubes (HNT) with the view to be utilized in a textile industrial effluent (TIE). The DB15 adsorbed-HNT “sludge” was used as a reinforcing agent and plastic waste to fabricate the composite. To advance the knowledge and further understand the chemical phenomena associated with DB15 adsorption on HNT, different factors like pH value, adsorbate initial concentration, adsorbent dosage, and temperature on the composite were affected experimentally tested. To estimate the adsorption capacity of HNT, nine isotherm models were applied, and it was identified that the Brouers–Sotolongo adsorption isotherm model represented the best accuracy for predicting the adsorption behavior of the HNT. Likewise, the pseudo-second-order reaction was the predominant mechanism for the overall rate of the multi-step dye adsorption process. Additionally, it was demonstrated that the mass transfer during the process is diffusion-controlled, and thermodynamic assessments showed that the process is physisorption.

Assessment and treatment of floodwater in the Vietnamese Mekong Delta using a simple filter system based on silver nanoparticles coated onto activated carbon derived from rice husk

The floods in the Vietnamese Mekong Delta have long caused a shortage of clean water supply, which has a significant impact on the indigenous people in the region. We have conducted a preliminary survey of the water quality of the Hau Giang River (one of the two main branches of the Mekong River) before, during, and after the flood season. The obtained results demonstrated that the water in the Hau Giang River was highly turbid and contaminated with a large number of harmful microorganisms. Thus, in this study, a simple filter system based on silver nanoparticles coated onto activated carbon derived from rice husk (AgNPs@AC) has been proposed for treating floodwater from the Hau Giang River. The optimal conditions for AgNPs@AC preparation were established. The prepared AgNPs@AC was then characterized using various surface analyses such as SEM, TEM, XRD, BET, FTIR, and DLS. The initial floodwater source would be pre-treated with polyaluminum chloride using the coagulation–sedimentation method to remove the suspended solids before being discharged into the filtration column containing AgNPs@AC. The results showed that the filter system based on AgNPs@AC performed well in removing turbidity, dissolved solids, suspended solids, color, and bacteria from the floodwater. In addition, it was determined that the filter column with a 30 mm thick AgNPs@AC layer could continuously process 1300 m³ of the floodwater and had a service life of more than two months. The findings of this study not only added to our understanding of the floodwater treatment capacity of activated carbon coated nanoparticles, but they also provided valuable information for water treatment plants along the Hau Giang River, aquatic ecosystem researchers, and public health researchers.

In this study, a simple filter system based on silver nanoparticles coated onto activated carbon derived from rice husk (AgNPs@AC) has been proposed for treating floodwater from the Hau Giang River.