Alternative Low-cost Adsorbent Research Articles

Food dye adsorption in single and ternary systems by the novel passion fruit peel biochar adsorbent

This study evaluated the passion fruit peel biochar (PFPB) as a novel adsorbent for synthetic food dyes indigotine blue (IB), tartrazine yellow (TY), and ponceau 4R (P4R) removal in single and ternary systems. A macroporous structure and a predominance of basic groups characterized PFPB. The pH study revealed better adsorption at pH 2.0. The response surface methodology optimization for adsorbent dosage and temperature predicted removal efficiencies of 100 % for IB, 79.8 % for TY, and 84.4 % for P4R. Elovich and Redlich-Peterson models better described kinetic and equilibrium, respectively, suggesting the contribution of chemical interactions. Thermodynamic data revealed endothermic, with an inordinate degree and spontaneous adsorption. In the ternary systems, antagonistic effects of interaction were noticed. The adsorption of synthetic effluents showed promising results with removal efficiencies of 99.6 % (IB), 60.2 % (TY), and 51.8 % (P4R). Therefore, we concluded that PFPB is a potential alternative low-cost synthetic food dye removal adsorbent.

Uptake of selected heavy metals from contaminated waters utilizing cost-effective and environmentally friendly biosorbents prepared from the residues of a traditionally fermented Ethiopian alcoholic beverage (Tella)

In the current study, the adsorption capacity of Tella residues (residues of fermented alcoholic beverage) for quantitative uptake of Cu(II), Cd(II), Zn(II) and Pb(II) was evaluated. Chemical treatment of the local beer residue (LBR) has improved the removal efficiency of the adsorbent, which was achieved at pH = 5, 1.0 g adsorbent, 50 mg/L initial concentration, 180 min contact time and agitation speed of 100 rpm. The adsorption was found to fit the Langmuir adsorption isotherm model, and the theoretical equilibrium capacities were well fitted with the experimental equilibrium capacities, resulting in chemical adsorption (chemisorptions) on the adsorbent surface while the equilibrium kinetics follows the pseudo-second-order. The adsorption capacity (Qo) of LBR decreases in the following order: Zn(II) > Cu(II) > Pb(II) > Cd(II) as metal concentration ranged from 20-200 mg/L. Thermodynamic parameters, including standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated to predict the nature of adsorption. The negative values of ΔG° and the positive value of ΔH° indicate that the adsorption process was spontaneous and endothermic. Adsorption capacities were found to increase when the temperature ranged from 25-60 °C. Thus, the findings suggest a promising application of LBR as an alternative low-cost novel adsorbent for the removal of toxic heavy metals from wastewater.

Enhancing hexavalent chromium removal from textile effluent with low-cost adsorbent: simulation and a techno-economic study

AbstractThis paper simulated hexavalent chromium (Cr(VI)) adsorption using cocoa pod husk biosorbent in a fixed bed column using Aspen Adsorption. This study was designed to show the effectiveness of computational methods in designing, optimising and evaluating the scaled-up adsorption process using low-cost adsorbents. To the best of our knowledge, the economic analysis of Cr(VI) removal using biosorbent adsorption columns with the assistance of Aspen Adsorption and response-surface methodology (RSM) has not been performed previously. Design Expert and RSM were used to optimise and describe the effect of flow rate and initial concentration on breakthrough and saturation times. The breakthrough time was improved by a higher bed height (2.0 m), a wider diameter (2.0 m), and lowering the flow rate (0.010 L/s). The initial concentration had no effect (1.00 mol/L). The predicted breakthrough and saturation time were 29,360 s and 313,351 s, respectively. Two scenarios were economically compared over 20 years. Scenario 1 (1-day breakthrough time) costs $746,585 and Scenario 2 (4-week breakthrough time) costs $1,538,319. This is because Scenario 2 used a taller, wider column which required a greater amount of adsorbent, and 387,873 m3 of water were processed, respectively. Processed water was dependent on the flow rate and breakthrough time. It was concluded that cocoa pod husk could be an efficient adsorbent and the adsorption process can be successfully simulated and optimised. The use of alternative low-cost adsorbents should be encouraged. The economic study showed that simulation and RSM data could successfully be used for economic analysis. Graphical abstract

KINETIC, ISOTHERM AND THERMODYNAMIC STUDIES OF THE ADSORPTION OF CRESOL RED DYE USING AGRICULTURAL WASTES

Agricultural wastes and plant biomass are alternative low-cost adsorbents because they can be used without or with a minimum processing. In the present study, batch experiments were carried out to study the adsorption of cresol red (CR) unto mango leaf (ML) and orange peel (OP). Several parameters that affect adsorption process such as pH, adsorbent dosage, contact time, initial dye concentration and temperature were investigated. FTIR and SEM were used to determine the functional group responsible for adsorption. The results revealed that the highest adsorption efficiency was at pH 5 for the two adsorbents. It was also discovered that CR removal efficiency increased with the increase in contact time and adsorbent dosage while adsorption capacity was higher with increase in initial dye concentration but removal efficiency was lowered. The kinetics conform with the pseudofirst-order kinetic model for mango leaf but conform with the pseudo-second-order kinetic for orange mesocarp due to the value of the correlation coefficient (R2). Based on the value of correlation coefficient, the experimental results for the removal by mango leaf best fitted the Langmuir isotherm model with monolayer adsorption capacity of 70.64 mg. g-1, while Freundlich isotherm model was best fitted to the experimental results for the adsorption of CR by Orange peel. The thermodynamic results revealed that the process is spontaneous and endothermic.

A review on sustainable management of biomass: physicochemical modification and its application for the removal of recalcitrant pollutants-challenges, opportunities, and future directions.

Adsorption is one of the most efficient methods for remediating industrial recalcitrant wastewater due to its simple design and low investment cost. However, the conventional adsorbents used in adsorption have several limitations, including high cost, low removal rates, secondary waste generation, and low regeneration ability. Hence, the focus of the research has shifted to developing alternative low-cost green adsorbents from renewable resources such as biomass. In this regard, the recent progress in the modification of biomass-derived adsorbents, which are rich in cellulosic content, through a variety of techniques, including chemical, physical, and thermal processes, has been critically reviewed in this paper. In addition, the practical applications of raw and modified biomass-based adsorbents for the treatment of industrial wastewater are discussed extensively. In a nutshell, the adsorption mechanism, particularly for real wastewater, and the effects of various modifications on biomass-based adsorbents have yet to be thoroughly studied, despite the extensive research efforts devoted to their innovation. Therefore, this review provides insight into future research needed in wastewater treatment utilizing biomass-based adsorbents, as well as the possibility of commercializing biomass-based adsorbents into viable products.

Thermodynamic interpretation of cationic dye adsorption onto untreated coffee residues as adsorbents via statistical physics approach

In this current paper, we perform a theoretical examination of adsorption systems undertaken through the application of statistical physics modeling to experimental data Remacryl Red TGL (BR) dye adsorption isotherms onto the untreated coffee residues (UCR) based adsorbents at 298–338 K range. The experimental values exhibited a strong agreement with the predicted values, and the developed model received high approval. Significant parameters are theoretically discussed such as thermodynamic, energetic, and stereographic factors which determine the (BR) adsorption onto UCR. In the pursuit of unraveling the adsorption mechanism, four different models are adopted: a monolayer with one energy (Model 1), a monolayer with two horizontal energies (Model 2), a monolayer with three energies (Model 3) and a double-layer with two vertical energies (Model 4). The analysis considered both steric and energetic parameters associated with the adsorption reaction, namely the number of adsorbed particles per site (n1 and n2), the receptor sites density (N1m and N2m), and the concentration at half-saturation. It appears that the experimental data aligns well with a monolayer model characterized by two energy states. The variations in these factors are examined in relation to the temperature of absorption isotherms. More importantly, the calculation of adsorption energies unequivocally pointed out that the adsorption process is of a chemisorptive nature. Our findings indicate that (UCR) could be utilized as a low-cost alternative adsorbent in wastewater treatment to eliminate the Remacryl Red TGL (BR) dye.

A Review on Biochar as an Adsorbent for Pb(II) Removal from Water

Heavy metal contamination in drinking water is a growing concern due to its severe health effects on humans. Among the many metals, lead (Pb), which is a toxic and harmful element, has the most widespread global distribution. Pb pollution is a major problem of water pollution in developing countries and nations. The most common sources of lead in drinking water are lead pipes, faucets, and plumbing fixtures. Adsorption is the most efficient method for metal removal, and activated carbon has been used widely in many applications as an effective adsorbent, but its high production costs have created the necessity for a low-cost alternative adsorbent. Biochar can be a cost-effective substitute for activated carbon in lead adsorption because of its porous structure, irregular surface, high surface-to-volume ratio, and presence of oxygenated functional groups. Extensive research has explored the remarkable potential of biochar in adsorbing Pb from water and wastewater through batch and column studies. Despite its efficacy in Pb removal, several challenges hinder the real application of biochar as an adsorbent. These challenges include variability in the adsorption capacity due to the diverse range of biomass feedstocks, production processes, pH dependence, potential desorption, or a leaching of Pb from the biochar back into the solution; the regeneration and reutilization of spent biochar; and a lack of studies on scalability issues for its application as an adsorbent. This manuscript aims to review the last ten years of research, highlighting the opportunities and engineering challenges associated with using biochar for Pb removal from water. Biochar production and activation methods, kinetics, adsorption isotherms, mechanisms, regeneration, and adsorption capacities with process conditions are discussed. The objective is to provide a comprehensive resource that can guide future researchers and practitioners in addressing engineering challenges.

Study on anionic dye toxicity reduction from simulated media by MnO2/agro-biomass based-AC composite adsorbent

In order to reduce the consequences of increased by-products generated by demand for plants essential oil extraction factories, it is important transforming such waste disposal into useful materials. Herein, efficient adsorbent from residues of Eucalyptus camaldulensis leaves (ECL-AC) supported αMnO2 was prepared by the redox reaction between Mn2+ and Mn7+ at approximatively neutral pH and ECL-AC to increase their interactions contributing to the enhanced adsorptive capacity for Helianthine from aqueous media. The by-product was simultaneously activated by impregnation in Potassium permanganate solution as oxidizing agent followed by heating in tubular furnace under controlled atmosphere, resulting in α-MnO2-AC adsorbent. Prior to removal tests, the prepared AC- MnO2 sample was characterized for functional groups (IRFT) and pores structure by evaluation the iodine number (IN) and methylene blue index (MBI). Parameters affecting Helianthine uptake such as equilibrium time, adsorbent dose, solution pH and temperature were also studied. Well known adsorption isotherm models namely, Langmuir, Freundlich and Temkin were used for data analysis and better described by Langmuir model with a maximum uptake of 64.71 mg/g at pH 2.08. The surface area estimation indicates that AC-MnO2 better described by Langmuir model. The surface area estimation indicates that MnO2-AC is microporous/mesoporous material. Calculated thermodynamic parameters showed that the adsorption of Helianthine dye onto MnO2-AC is a spontaneous and exothermic process. Results indicate that this doped biomass based-activated carbon can be used successfully as an alternative low-cost adsorbent in the removal of Helianthine from industrial effluents.

Adsorption studies of dye molecule on two-dimensional assembly of porphyrin using density functional theory

<p>Highly toxic dye molecules can be found in trace amounts in the treated effluent from several industrial wastes. A challenging research area of this decade is the dye treatment and adsorption from the effluents of these industries using low-cost alternative adsorbents. Recent studies have demonstrated the effectiveness of metal oxides and porous materials in the adsorption of dye, so we have taken into consideration an organic porous material made with metal free porphyrin. The adsorption of dye molecules on the surface of the porphyrin sheet is investigated. Porphyrin is an organic substance with several special properties. Density functional theory (DFT) is used to investigate the adsorption of charged and neutral dye, as well as complex heavy metal dye, on the surface of porphyrin sheets. Positive dye has a higher affinity for the adsorbent than negative dye, according to the data on adsorption; however, complex dye has a higher adsorption energy than the other dyes, which is consistent with the cohesive energy of the PS-dye complex. In the present work the adsorbing capacity of PS for different dye molecules is demonstrated by the topological analysis and DFT calculations on the electronic structure.</p>

Comparison of activated carbon and low-cost adsorbents for removal of 2,4-dichlorophenol from wastewater using Aspen Adsorption and response surface methodology

ABSTRACT In this paper, the adsorption of the chlorinated organic compound, 2,4-dichlorophenol, using activated carbon (AC), bagasse fly ash (BFA) and rice husk fly ash (RHFA) in a packed bed column was simulated using Aspen Adsorption software. The purpose of this study was to demonstrate the effectiveness of simulation software for identifying alternative low-cost adsorbents and optimising the adsorption process. The effect of process parameters such as initial concentration, bed height and inlet feed flow rate were evaluated using breakthrough curves. It was shown that the longest breakthrough times were at a higher bed height of 3 m and lower flow rate of 2 m3/hr and concentration had no effect on breakthrough time. After optimisation using response surface methodology, the AC, BFA and RHFA had a breakthrough time of 534, 426 and 209 s, respectively. This shows the potential of BFA as a potential alternative for AC for the adsorption of 2,4-dichlorophenol and shows RHFA to be a relatively poor adsorbent in comparison. The economic evaluation illustrates that the overall cost of wastewater treatment with BFA and RHFA is lower than AC. The cost for the BFA and RHFA adsorbents is only a handling charge, but the cost for using AC adsorbent is £10,603/year. Therefore, the company can produce 17,520 m3/year of fresh water from the adsorbent and save £87,600/year. Therefore, it was concluded that BFA had a slightly weaker adsorption efficiency than AC but was more cost effective, allowing it to be more affordable and increasing its availability.

Removal of endosulfan from water by municipal waste incineration fly ash-based geopolymers: Adsorption kinetics, isotherms, and thermodynamics

Alkali-activated municipal waste incineration fly ash (MWFA)-based geopolymers (GPA, GPB, and GPC) were synthesized under different sodium silicate to sodium hydroxide (SS/SH) ratios. The geopolymers were applied in the removal of endosulfan, a persistent and toxic chemical, from water. The adsorbents were characterized by XRD, SEM-EDX, and FTIR. Variation of SS/SH ratios resulted in morphologically distinguishable geopolymers with different compositions. The adsorption equilibrium data were best described by the Langmuir isotherm. The maximum adsorption capacities increased with an increase in SS/SH ratios in the order 1.87, 15.89, 16.97, and 20.01 mg/g for MWFA, GPA, GPB, and GPC, respectively. The kinetic data were best described by the pseudo-first-order model wherein the adsorption rate (k1) was independent of the SS/SH ratios and the geopolymer composition. The thermodynamic parameters, that is, enthalpy (∆H > 0), Gibbs free energy (∆G < 0), entropy (∆S > 0), and activation energy (Ea > 0), show that the processes were endothermic, spontaneous, physical (Ea and ∆H < 40 kJ/mol), and entropy-driven. Alkalination was beneficial since the geopolymers had a higher adsorption capacity (∼8–10 times) and affinity for endosulfan (∼30 times) than the precursor material (MWFA). The adsorption mechanism entailed electrostatic interactions and hydrogen bonding. The MWFA-based geopolymers are, therefore, potential alternative low-cost adsorbents for the removal of endosulfan from water and a strategy for the valorization of MWFA.

Evaluation of humic acid embedded Chitosan/PVA composite performance in the removal of uranyl ions

In this study, the retention of uranyl ions on a novel, natural and cost-effective adsorbent, humic acid (HA) embedded chitosan/polyvinyl alcohol (Ch/PVA-HA) bio composite was investigated. The highest adsorption capacity reported in literature was achieved by Ch/PVA-HA in a column system in this study. Specific surface area of Ch/PVA-HA was found as 1.308 m2g-1 which is rather high comparing that of Ch/PVA (0.254 m2g-1). The maximum adsorption on Ch/PVA and Ch/PVA-HA were achieved in the range of 1 < pH < 5, and 1 < pH < 4, respectively. The batch tests showed that adsorption isotherm of uranyl ions was changed from Freundlich to Langmuir when the surface of Ch/PVA copolymer was covered with HA. The maximum uranyl adsorption capacity of Ch/PVA-HA was found as 37.8 mg/g while the column capacity was 1909 mg/g. The presence of HA enhanced the distribution ratio of uranyl ions between adsorbent phase and aqueous solution. Considering the results of the batch and column tests, it can be said that the Ch/PVA-HA may have high potential to use as alternative low-cost adsorbent for removal of uranyl ions. Also, this study will lead up synthesis of new adsorbents to provide higher and recoverable uranyl adsorption.

Evaluation of TiO2/smectite nanoparticles as an alternative low-cost adsorbent for chromium removal from industrial wastewater

Evaluation of TiO2/smectite nanoparticles as an alternative low-cost adsorbent for chromium removal from industrial wastewater

Removal of Cu (II) via chitosan-conjugated iodate porous adsorbent: Kinetics, thermodynamics, and exploration of real wastewater sample

Remediation of copper (II) pollutant in aquatic ecosystems is a long-standing concern in the field of water management and the subject of intensive research. In this study, chitosan conjugated iodate porous material (CS-CI) was successfully prepared by media (ammonia, acetic acid, and absolute ethanol) and was used in the treatment of Cu (II) in wastewater samples. Different methods were applied to characterize the CS-CI, including FTIR, SEM, XRD, and TGA. The result showed significant improvement in surface properties and stability when the chitosan was conjugated with the iodate. The adsorption of Cu (II) followed the pseudo-first-order kinetic model and Langmuir isotherm model with a maximum adsorption capacity of 95.2 mg/g. In a complex system (real wastewater), the CS-CI took advantage of the adsorptive properties of both chitosan (CS) and the iodate to significantly improved the remediation of Cu (II) in aqueous media. Therefore, the synthesized chitosan conjugated iodate porous material is promising as an alternative low-cost adsorbent for the treatment of copper (II) in wastewater.

Activated carbon from H3PO4 -activated Moringa Stenopetale Seed Husk for removal of methylene blue: Optimization using the response surface method (RSM)

In this study, an alternative precursor for production of activated carbon was introduced using Moringa Stenopetale Seed Husk (MSSH). Moreover, H 3 PO 4 was used as a chemical activator in the thermal carbonization process to convert MSSH into activated carbon. The prepared adsorbent was characterized using proximate analysis and Instrumental like FT-IR, SEM/EDX, and XRD. The optimization process was developed using the Box-Behnken methodology (BBM) and the response surface method (RSM). Analysis of variance (ANOVA) revealed a good agreement between experimental and predicted value. Investigation of the processing parameters was done using the batch adsorption method. The optimal conditions for removing methylene blue were found to be the initial dye concentration (316 mg/L), contact duration (19.3 min), adsorbent dosage (0.055 g), and shaking speed (176 rpm). Maximum efficacy was found to be 99.4%, and the highest adsorption capacity was 436.68 mg/g. The experimental results have been best fitted well by the Langmuir isotherm model with the higher correlation coefficients of R 2 = 0.954 rather than Freundlich and Temkin adsorption isotherm. This indicates that the process followed homogenous adsorption of adsorbate on the surface of adsorbent. The adsorption kinetics was best fitted with pseudo-second order kinetics. The result of thermodynamic parameters showed that a negative value of ΔG o and positive ΔH o confirms the spontaneous and endothermic nature of the adsorption of MB onto the adsorbents. The positive values of ΔS o indicate the increase in randomness of at the solid-liquid interface during the adsorption process. Generally, the results indicate that activated carbon prepared from MSSH can be used as a low cost, easily applicable and eco-friendly alternative adsorbent for treatment of effluents containing MB dye. • Activated Carbon was prepared form Moringa stenopetale seed husk. • The Activated carbon prepared was characterized by proximate value and analytical instruments. • The Response surface methodology (RSM) and Box-Behnken approach were used to create the optimization procedure. • Different Adsorption parameters and Adsorption models was Conducted. • The highest adsorption capacity was 436.68 mg/g, and maximum efficacy was found to be 99.4%

Adsorption of Pb(II) from aqueous solution using alkaline-treated natural zeolite: Process optimization analysis

• Alkaline-treated zeolite was successfully prepared and applied for Pb(II) removal. • Factors influenced Pb(II) removal, Y : pH, X 2 > adsorbent dosage, X 3 > initial concentration, X 1. • Optimum conditions: X 1 = 240 mg/L, X 2 = 6, and X 3 = 1.07 g/L , Y = 60.75% • Alkaline-treated zeolite showed good regeneration and reusability up to 3 cycles. Alkaline-treated natural zeolite was prepared by sodium hydroxide treatment of natural zeolite and applied in the adsorption of Pb(II). The response surface methodology (RSM) analysis was conducted under manipulated variables of initial concentration ( X 1 = 50-400 mg/L), pH ( X 2 = 2-10), and adsorbent dosage ( X 3 = 0.5-5.0 g/L). The optimal condition was attained at X 1 = 240 mg/L, X 2 = 6, and X 3 = 1.07 g/L, with Pb(II) removal of 60.75%. The characterization of alkaline-treated natural zeolite of fresh and spent confirmed the adsorption of Pb(II) onto alkaline-treated natural zeolite. The reusability and regeneration experiments revealed the ability of the alkaline-treated natural zeolite in multiple cycles of the adsorption process. This study proved that alkaline-treated natural zeolite could be an alternative low-cost adsorbent for wastewater treatment containing Pb(II).

Removal of Tryphenylmethane Dyes by the Microalgae Chlorella sp.

Removal of organic dyes from industrial wastewater is a costly process. Activated charcoal and polymeric material are widely used to adsorb such material. Biomass provides alternative low-cost adsorbents to remove organic substances in wastewater. Dry biomass is only capable of adsorption, whereas live biomass is capable of adsorption as well as degradation of molecules to less toxic substances. Bioremediation with microalgae (phycoremediation) is a practically useful approach due to the ease of handling and environmental adaptability of microalgae. This study was aimed to use phycoremediation to remove tryphenylmethane dyes; crystal violet, methyl violet, malachite green, and fuchsin from aqueous solutions using microalgae Chlorella sp. The microalgae samples were extracted from polluted water bodies in Kandy urban area. To determine the factors affecting the dye removal, the percentage decolorization was determined at different salt concentrations by measuring UV-visible absorption at appropriate wavelengths. NaCl was used as the representative inorganic salt. Chlorella sp. showed tolerance up to 2,000 ppm salt concentrations and was able to decolorize dye solutions above 60% within five days. Three replicates were done under each salt concentration. Further, the effect of dye concentration on the decolorization rate was investigated for five different salt concentrations from 0 ppm to 500 ppm. Chlorella sp. showed a decolorization percentage above 65% in the presence of 100 ppm dye concentrations. The phycoremediation potential of Chlorella sp. was determined by investigating the change in pH, chemical oxygen demand (COD), and phosphate content after the treatment using simulated wastewater. The microalgae were able to maintain the pH levels within the discharge limits. The chemical oxygen demand was decreased from a value around 600 mgL-1 to a value less than 250 mgL-1 which was within the discharge limits. Phosphate content was also decreased within 10 days. According to the above study, it can be concluded that the isolated Chlorella sp. can be used to treat and improve the quality of wastewater contaminated with tryphenylmethane dyes.&#x0D; Keywords: Chlorella sp., Tryphenylmethane dyes, Decolorization, Phycoremediation

Statistical optimization of Methylene Blue dye removal from a synthetic textile wastewater using indigenous adsorbents

This study was carried out to determine the most suitable indigenous adsorbents to remove Methylene Blue (MB) dye from aqueous solution and to statistically optimize the removal process parameters. Experiments were performed to investigate the adsorption capacities of indigenous bio-adsorbents such as charcoal, banana leaves ash (BLA), coconut coal, neem seed and rice husk ash to remove dye from industrial effluent. The dye removal process parameters were optimized using the One-Factor-at-a-Time (OFAT) method and statistically using central composite design (CCD). Banana leaves ash with particle sizes of 0.053–0.075 mm was found to be a potential adsorbent for dye removal. Among six parameters pH, incubation temperature and particle size were fixed at 8.7 (without control), 30 ± 0.5 °C (ambient) and 0.053–0.075 mm, respectively from the experimental results using the OFAT method. The other three parameters, adsorbent dose, shaking time and shaking speed were finally optimized statistically. The highest removal of MB (93.75%) was obtained through the statistical experimental design at optimum conditions of 23.9 mg/100 ml adsorbent (BLA) dose, 3 h shaking time and 356 rpm shaking speed. The ANOVA showed that the developed model is highly significant with an R 2 value of 0.99. All model terms are also highly significant (p-value<0.01, except for the interactive terms ‘adsorbent dose’ and ‘shaking time’ (p-value<0.05) (also significance at 5% confidence level). The validation experiment demonstrated great similarity between predicted and experimental results. The study indicates that BLA could be employed as a low-cost alternative adsorbent in wastewater treatment to remove dyes.

Cellulose, clay and sodium alginate composites for the removal of methylene blue dye: Experimental and DFT studies

Cellulose/clay/sodium alginate composites were prepared and employed for the removal of methylene blue (MB) dye. Cellulose was extracted from a paper mill waste and used for composite preparation with sodium alginate (Na-Alg) and clay. MB dye removal was analyzed at different operating conditions (pH, initial concentration, temperature, composite dose). The dye was adsorbed up to 90% for an equilibrium time of 60 min at optimum level of adsorbent dose (0.05 g), temperature (30 °C) and pH (i.e., 7 and 11 for cellulose-Na-Alg and cellulose-Na-Alg-clay, respectively). Kinetics and isotherms of MB adsorption were quantified and modeled. Results showed that MB dye adsorption data followed the pseudo-first order kinetics and a statistical physics model was used to analyze the adsorption mechanism. Thermodynamic calculation revealed that the MB dye adsorption on these composites was an exothermic, spontaneous and feasible process. The composites were regenerated with HCl thus contributing to their reutilization in subsequent adsorption cycles. The DFT (density functional theory) calculations were executed to explain the interactions responsible for the adsorption of MB dye on the composites. Results revealed that the Na-Alg-cellulose composites were effective for the MB dye removal. Therefore, these composites can be considered as low-cost alternative adsorbents for the pollution remediation caused by dyes in industrial effluents.

Adsorption and desorption of phosphate onto chemically and thermochemically pre-activated red ceramic waste: Characteristics, batch studies, and mechanisms

The knowledge of adsorption and desorption mechanisms of phosphate onto construction wastes is important to minimize environmental concerns related to its discharge into water. In this study, we verified the adsorption and desorption capacity of red ceramic waste in the removal of phosphate from aqueous solution, unmodified (RC), chemically (CAC, dolomite lime) and thermochemically (TCAC, heated/dolomite lime) pre-activated. Adsorption process was best described by pseudo-first-order kinetic model for RC (1.22 mg g−1) and CAC (3.59 mg g−1) and by pseudo-second-order model for TCAC (4.57 mg g−1) at pH 5.3. Pseudo-second-order model better described desorption for RC (1.13 mg g−1) and pseudo-first-order model for CAC (0.54 mg g−1) and TCAC (0.54 mg g−1) at pH 13.3. Regarding the maximum adsorption capacities, Langmuir model best fitted to RC with 2.27 mg g−1; Freundlich model to CAC with 4.10 mg g−1; and Sips model to TCAC with 22.28 mg g−1 at pH 5.3. Sips model was best fitted to the desorption equilibrium data with 16.72 mg g−1 for RC, 15.45 mg g−1 for CAC, and 5.20 mg g−1 for TCAC at pH 13.3. The negative ΔH° showed the exothermic nature of adsorption for RC (−159.75 kJ mol−1), CAC (−108.59 kJ mol−1) and TCAC (−102.89 kJ mol−1). For desorption, the exothermic nature was verified for RC (−34.06 kJ mol−1) and TCAC (−44.11 kJ mol−1); while endothermic process was noted for CAC (9.61 kJ mol−1). Finally, the red ceramic, both unmodified and pre-activated, could be used as alternative low-cost adsorbent in the removal of phosphate.