Rhodamine B removal with activated carbons obtained from lignocellulosic waste

Hierarchical Porous Activated Carbon from Wheat Bran Agro-Waste: Applications in Carbon Dioxide Capture, Dye Removal, Oxygen and Hydrogen Evolution Reactions

This work reports an efficient method for facile synthesis of hierarchically porous carbon (WB-AC) utilizing wheat bran waste. Obtained carbon showed 2.47 mmol g-1 CO2 capture capacity with good CO2 /N2 selectivity and 27.35 to 29.90 kJ mol-1 isosteric heat of adsorption. Rapid removal of MO dye was observed with a capacity of ~555 mg g-1 . Moreover, WB-AC demonstrated a good OER activity with 0.35 V low overpotential at 5 mA cm-2 and a Tafel slope of 115 mV dec-1 . It also exhibited high electrocatalytic HER activity with 57 mV overpotential at 10 mA cm-2 and a Tafel slope of 82.6 mV dec-1 . The large SSA (757 m2  g-1 ) and total pore volume (0.3696 cm3  g-1 ) result from N2 activation contributing to selective CO2 uptake, high and rapid dye removal capacity and superior electrochemical activity (OER/HER), suggesting the use of WB-AC as cost effective adsorbent and metal free electrocatalyst.

Comprehensive analysis of cationic dye removal from synthetic and industrial wastewater using a semi-natural curcumin grafted biochar/poly acrylic acid composite hydrogel

Polymer composites offer a tailored framework as an exceptional candidate for water treatment due to their tunable chemical structure, porous 3D architecture, physiochemical stability, accessibility, pH-sensitivity and ease of use. In this study, curcumin-engineered biochar is embedded into a cross-linked polyacrylic acid hydrogel matrix using in situ polymerization for developing a semi-natural adsorbent for the removal of cationic dye from an aqueous solution. The physicochemical features of the generated composite hydrogel are significantly influenced by the implementation of curcumin-grafted biochar into the polyacrylic acid substrate. Comprehensive characteristic approaches were employed to explore all aspects of the adsorbent's properties, especially its removal efficacy. The methodical adsorption study was accomplished by monitoring dynamic factors such as pH, adsorbent content, time frame, and initial dye concentration. The presence of the porous aromatized structure of biochar, active oxygen-enrich functional groups (carboxyl, hydroxyl, keto, enol, ether) coupled with the conjugated curcumin structure facilitate the effective establishment of hydrogen bonds, electrostatic interactions, π-π interactions, electron donor-acceptor and charge-assisted H-bonding with the malachite green (MG) and rhodamine B (Rho) molecules. The highest adsorption capacities of MG and Rho reached 521 mg g-1 and 741 mg g-1 respectively, in the range of neutral pH, considering their molecular nature, functionalities, and unique adsorption mechanisms. The isothermal modeling was carried out with Henry, Langmuir, Jovanovic, Freundlich, Temkin, and Koble-Corrigan models to determine the adsorption system. Additionally, the kinetic data were assessed with Bangham, pseudo-first-order, pseudo-second-order, intra-particle, and liquid film diffusion models to ascertain the rate-limiting phase. The Koble-Corrigan and Langmuir isotherm models (R2 > 0.997) as well as pseudo-second-order (R2 > 0.998) and Elovich (R2 = 0.983 and 0.995) kinetics models provide a substantial level of concordance with empirical findings. The analysis of non-linear diffusion models revealed that the Bangham (R2 > 0.995) pore and liquid film diffusion (R2 > 0.960) models has major influence on the rate of the adsorption procedure. The binary adsorption test demonstrated higher efficacy of the synthesized adsorbent in the removal of malachite as compared to rhodamine. This study sheds light on the design of a cost-effective semi-natural polymeric composite for treating dye-polluted wastewaters, a major milestone toward environmental and ecological sustainability.

Rapid removal of Rhodamine B by phosphoric acid-modified activated carbon derived from rape straw

A series of activated carbon was obtained from rape straw by chemical modification with phosphoric acid (H3PO4). The activated carbon was characterized and the adsorption capacity for Rhodamine B (RhB) from water was analysed. The SEM images showed that PRC-40 is a porous material and the BET analysis revealed a high surface area of 1720 m2/g with the coexistence of micropores and mesopores. The FTIR spectra determined the presence of oxygenated functional groups at its surface. The XPS spectra revealed that the content of carboxyl and metaphosphate groups in the modified activated carbon significantly increased, and this is conducive to the adsorption reaction. The XRD pattern showed the amorphous nature of carbon. The effect of significant parameters, such as the concentration of H3PO4 for modification and pH value, has been discussed. The kinetic data showed that the pseudo-second-order model is predominant. Besides, the Langmuir model was compatible well with the equilibrium data, and the maximum adsorption capacity of the activated carbon modified by H3PO4 was 2882.84 mg/g. Therefore, agricultural waste and rape straw can be used to prepare effective adsorbents for the application with the removal of dye from wastewater.

Efficient benzo(a)pyrene degradation by coal gangue-based catalytic material for peroxymonosulfate activation

A low cost and green peroxymonosulfate (PMS) activation catalyst (CG-Ca-N) was successfully prepared with coal gangue (CG), calcium chloride, and melamine as activator. Under the optimal conditions, the CG-Ca-N can remove 100 % for benzo(a)pyrene (Bap) in an aqueous solution after 20 min and 72.06 % in soil slurry medium within 60 min, which also display excellent reuse ability toward Bap after three times. The removal of Bap is significantly decreased when the initial pH value was greater than 9 and obviously inhibited in the presence of HCO3- or SO42-. The characterization results indicated that the addition of calcium chloride could stabilize and increase the content of pyridinic N during thermal annealing, resulting in the production of •OH, SO4•- and 1O2. Based on electron paramagnetic resonance (EPR) and active radical scavenging experiments, 1O2 could be identified to be the dominant role in Bap degradation. Overall, this work opened a new perspective for the low cost and green PMS catalysts and offered great promise in the practical remediation of organic pollution of groundwater and soil.

Interpretation of the adsorption process of toxic Cd2+ removal by modified sweet potato residue

Cadmium (Cd) is a common and toxic non-essential heavy metal that must be effectively treated to reduce its threat to the environment and public health. Adsorption with an adsorbent, such as agricultural waste, is widely used to remove heavy metals from wastewater. Sweet potato, the sixth most abundant food crop worldwide, produces a large amount of waste during postharvest processing that could be used as an economic adsorbent. In this study, the feasibility of using sweet potato residue (SPR) as an adsorbent for Cd2+ adsorption was assessed. To enhance the removal rate, SPR was modified with NaOH, and the effects of the modification and adsorption conditions on the removal of Cd2+ from wastewater were investigated. The results showed that modified sweet potato residue (MSPR) could be adapted to various pH and temperatures of simulated wastewater, implying its potential for multi-faceted application. Under optimized conditions, the removal of Cd2+ by MSPR was up to 98.94% with a maximum adsorption capacity of 19.81 mg g-1. Further investigation showed that the MSPR exhibited rich functional groups, a loose surface, and a mesoporous structure, resulting in advantageous characteristics for the adsorption of Cd2+. In addition, the MSPR adsorbed Cd2+ by complexation, ion exchange, and precipitation during a monolayer chemisorption adsorption process. This work demonstrates a sustainable and environment friendly strategy for Cd2+ removal from wastewater and a simple approach for the preparation of MSPR and also revealed the adsorption mechanism of Cd2+ by MSPR, thus providing a suitable adsorbent and strategy for the removal of other heavy metals.

Multiscale Porous Carbon Materials by In Situ Growth of Metal-Organic Framework in the Micro-Channel of Delignified Wood for High-Performance Water Purification

Porous carbon materials are suitable as highly efficient adsorbents for the treatment of organic pollutants in wastewater. In this study, we developed multiscale porous and heteroatom (O, N)-doped activated carbon aerogels (CAs) based on mesoporous zeolitic imidazolate framework-8 (ZIF-8) nanocrystals and wood using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation, in situ synthesis, and carbonization/activation. The surface carboxyl groups in a TEMPO-oxidized wood (TW) can provide considerably large nucleation sites for ZIF-8. Consequently, ZIF-8, with excellent porosity, was successfully loaded into the TW via in situ growth to enhance the specific surface area and enable heteroatom doping. Thereafter, the ZIF-8-loaded TW was subjected to a direct carbonization/activation process, and the obtained activated CA, denoted as ZIF-8/TW-CA, exhibited a highly interconnected porous structure containing multiscale (micro, meso, and macro) pores. Additionally, the resultant ZIF-8/TW-CA exhibited a low density, high specific surface area, and excellent organic dye adsorption capacity of 56.0 mg cm-3, 785.8 m2 g-1, and 169.4 mg g-1, respectively. Given its sustainable, scalable, and low-cost wood platform, the proposed high-performance CA is expected to enable the substantial expansion of strategies for environmental protection, energy storage, and catalysis.

Conversion of waste biomass to designed and tailored activated chars with valuable properties for adsorption and electrochemical applications

Waste biomass, a renewable energy source, is inexpensive material that has great potential in sorption and electrochemical application. The selected waste materials (corncobs, coconut shells, walnuts, and pistachio husks) allow to close the production cycle and enable material recycling, which are important aspects in the hierarchy of waste management. The proposed methodology for production and activation of biochars can be used industrially due to highly porous structure, developed surface area, and sorption ability of the obtained activated carbons (AC). A significant increase (from 4 up to more than 10 times) in specific surface area (SSA) is observed for all samples after the CO2 activation process (0.5 h at 800 °C) up to 725 m2 g-1 for corncobs, 534.9 m2 g-1 for pistachio husks, 523 m2 g-1 for coconut shells, and 393 m2 g-1 for walnut husks. The highest value of SSA is achieved for the AC derived from corncobs. This material is evaluated for use as an adsorbent, revealing 99% removal of Rhodamine B (dye/AC ratio of 0.0017) and 69% removal of chromium (dye/AC ratio of 0.0028). Based on the adsorption kinetics analysis, it is demonstrated that the Cr(VI) undergoes physical adsorption, while RhB undergoes chemisorption. In addition, corncob-derived AC exhibits superior electrochemical performance in 6 M KOH compared to the nonactivated biochar. A specific capacitance of 70 F g-1 at 5 A g-1 is achieved, along with outstanding rate capability (45 F g-1 at 50 A g-1) and cycling stability (94% at 10 A g-1 after 10,000 cycles). In contrast, the nonactivated sample shows only 34 F g-1 at 5 A g-1 and 13 F g-1 at 50 A g-1, with a stability of 91.4%.

The Influence of Oxidation and Nitrogenation on the Physicochemical Properties and Sorption Capacity of Activated Biocarbons Prepared from the Elderberry Inflorescence

The main objective of the study was to prepare a series of new activated biocarbons by means of physical and chemical activation of elderberry inflorescence. The influence of carbon matrix nitrogenation/oxidation on the physicochemical properties and sorption abilities of the carbonaceous materials was investigated. The impact of initial dye concentration, pH and temperature of the system on methylene blue and rhodamine B removal efficiency was checked. It was shown that activation of elderberry inflorescences with CO₂ or H₃PO₄, and their further modification by introducing nitrogen or oxygen functional groups, allowed us obtain a wide range of materials that differ significantly in terms of the chemical nature of the surface, degree of specific surface development and the type of porous structure generated. The samples prepared by chemical activation proved to be very effective in terms of cationic dyes adsorption. The maximum sorption capacity toward methylene blue and rhodamine B reached the level of 277.8 and 98.1 mg/g, respectively. A better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. It was also shown that the efficiency of methylene blue and rhodamine B adsorption from aqueous solutions decreased with increasing temperature of the system.

Preferential, synergistic sorption and reduction of Cr(VI) from chromium-rhodamine B mixed wastewater by magnetic porous biochar derived from wasted Myriophyllum aquaticum biomass

Eradication of heavy metals and dyes simultaneously from wastewater is urgently needed to safeguard public and environmental health. In this study, magnetic porous biochar derived from wasted Myriophyllum aquaticum (MPMaB) was synthesized by KOH-activation and co-precipitation method to treat chromate and rhodamine B (RhB)-bearing wastewater. The KOH activation significantly improved the pore structure of biochar with a high specific surface area of 937.1 m² g^-1. The sorption performance of MPMaB for Cr(VI) and RhB in single and co-solutes conditions was evaluated. In single system, a pH-dependent sorption pattern for Cr(VI) by MPMaB was revealed and the estimated sorption capability reached 175.4 mg g^-1, whereas the Langmuir-based sorption capacity of RhB was 175.4 mg g^-1 pH-independently. MPMaB partially transformed Cr(VI) to less toxic Cr(III) (approximately 59.3%). Synergistic sorption of Cr(VI) with the coexistence of RhB was observed, where synergistic effect ranged from 119% to 527% depending on pH. For example, the sorption capacity of Cr(VI) on MPMaB, at pH 2, augmented from 175.4 mg g^-1 (single system) to 208.3 mg g^-1 (binary system). Preferential sorption of Cr(VI) was found and was further confirmed by the post-sorption of Cr(VI) (or RhB) by MPMaB pre-sorbed with RhB (or chromate). Chromate sorption mechanisms mainly include electrostatic interactions and complexation, while the sorption of RhB is ascribed to π-π interactions, pore filling and hydrogen bonding. Additionally, MPMaB showed excellent reusability and maintained high removal efficiency after 5 cycles. In short, MPMaB can efficiently treat chromium and dyes-containing wastewater as sustainable and environmentally friendly adsorbent.

Oxygen-Rich Carbon Nitrides from an Eutectic Template Strategy Stabilize Ni, Fe Nanosites for Electrocatalytic Oxygen Evolution

Functionalized porous carbons are central to various important applications such as energy storage and conversion. Here, a simple synthetic route to prepare oxygen-rich carbon nitrides (CNOs) decorated with stable Ni and Fe-nanosites is demonstrated. The CNOs are prepared via a salt templating method using ribose and adenine as precursors and CaCl₂ ·2H₂ O as a template. The formation of supramolecular eutectic complexes between CaCl₂ ·2H₂ O and ribose at relatively low temperatures facilitates the formation of a homogeneous starting mixture, promotes the condensation of ribose through the dehydrating effect of CaCl₂ ·2H₂ O to covalent frameworks, and finally generates homogeneous CNOs. As a specific of the recipe, the condensation of the precursors at higher temperatures and the removal of water promotes the recrystallization of CaCl₂ (T < T_m = 772 °C), which then acts as a hard porogen. Due to salt catalysis, CNOs with oxygen and nitrogen contents as high as 12 and 20 wt%, respectively, can be obtained, while heteroatom content stayed about unchanged even at higher temperatures of synthesis, pointing to the extraordinarily high stability of the materials. After decorating Ni and Fe-nanosites onto the CNOs, the materials exhibit high activity and stability for electrochemical oxygen evolution reaction with an overpotential of 351 mV.

Efficient and easily scaled-up biosorbent based on natural and chemically modified macauba (Acrocomia aculeata) to remove Al3+, Mn2+ and Fe3+ from surface water contaminated with iron mining tailings

The ruptures of tailings mine dams in the cities of Mariana and Brumadinho contaminated local Brazilian Rivers with toxic metals. Herein, we describe a scaled-up biosorbent based on natural macauba endocarp (NTE) and macauba endocarp chemically treated (TE) to remove Al³⁺, Mn²⁺ and Fe³⁺ from aqueous solutions. For the TE material: the variation of pH and temperature of water did not cause significant sorption interferences; the kinetics studies suggest a pseudo-second-order model; the adsorption isotherms revealed that the Langmuir equation was the best fit for Al³⁺ and Mn²⁺, while the Freundlich equation best described the Fe³⁺; and the maximum adsorption capacities were between 0.268 mg g^-1 and 1.379 mg g^-1. A scaled-up was carried out using an adsorption column to remove the metals from Rio Paraopeba River water samples and the results showed that both NTE and TE are potentially low cost biosorbents for removing Al³⁺, Mn²⁺ and Fe³⁺.

Compounds based on iron mining tailing dams and activated carbon from macauba palm for removal of emerging contaminants and phosphate from aqueous systems

In this work, an iron-rich residue, which is widely obtained as a by-product in the iron mining industry, and macauba endocarp, waste from the extraction of vegetable oil for the production of biofuels, were used in the preparation of different composites based on iron and carbon. The composites were obtained by manual grinding of the calcined iron residue and activated carbon prepared by the macauba endocarp followed by thermal treatment under nitrogen atmosphere. The effect of the thermal treatment was analyzed by Mössbauer spectroscopy and X-ray diffraction and showed that the increase in the treatment temperature promoted the formation of different reduced iron phases in the final composite, such as Fe₃O₄, FeO, and Fe⁰. These composites were used in a combined adsorption/oxidation process through photocatalysis to remove up to 93% of amoxicillin from aqueous phase. The formation of possible reaction intermediates was monitored by electrospray ionization mass spectrometry (ESI-MS) and a mechanism of amoxicillin degradation was proposed. Afterward, the Fe/C composites were conducted to evaluate the impact of several parameters on phosphate adsorption processes and showed a maximum adsorption capacity of 40.3 mg g^-1. The adsorption capacity obtained for all the materials were greater than those found in the literature.

Influence of the surface modification of granular-activated carbon synthesized from macauba on heavy metal sorption

Adsorption on activated carbon is a promising technique for the treatment of low-concentration heavy metal pollutants in water with high efficiency and simple operation. However, commercial-activated carbon is often associated with high costs. Therefore, much attention has been given to activated carbon derived from low-cost agricultural and residual biomass. In this work, adsorption of Zn, Cd, and Pb ions in aqueous solutions was conducted using granular-activated carbon obtained from macauba palm, biomass waste of biofuel production, after surface modification using different methods. The adsorbents were obtained in granular form which facilitates all steps of the use, recovery, and reuse of the material, differently from the powdered-activated carbon normally used. The materials were characterized by using XPS, elemental analysis, N₂ sorption (BET method), and zeta potential measurements. Such techniques allowed observation of the functionalization of the carbon surface. The materials presented high adsorption capacities when compared to other works in the literature, with a capacity of approximately 7.69, 8.42, and 1.63 mmol g^-1 for Zn²⁺, Cd²⁺, and Pb²⁺, respectively. In addition, the materials showed a high capacity to be reused, removing 75% of Pb and 99% of both Cd and Zn after 4 cycles.

Ultrasonic spray pyrolysis synthesis of TiO2/Al2O3 microspheres with enhanced removal efficiency towards toxic industrial dyes

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry. In this study, TiO₂-modified Al₂O₃ microspheres with different TiO₂ contents were produced by spray pyrolysis, which is rapid and easy to scale up. Results reveal that the modification of γ-Al₂O₃ with TiO₂ reduced the crystallite size of Al₂O₃ and generated more active sites in the composite sample. The as-synthesized Al₂O₃-TiO₂ microspheres were applied to remove anionic methyl orange (MO) and cationic rhodamine B (RB) dyes in an aqueous solution using batch and continuous flow column sorption processes. Results show that the Al₂O₃ microspheres modified with 15 wt% of TiO₂ exhibited the maximum adsorbing capacity of ∼41.15 mg g^-1 and ∼32.28 mg g^-1 for MO and RB, respectively, exceeding the bare γ-Al₂O₃ and TiO₂. The impact of environmental complexities on the material's reactivity for the organic pollutants was further delineated by adjusting the pH and adding coexisting ions. At pH ∼5.5, the TiO₂/Al₂O₃ microspheres showed higher sorption selectivity towards MO. In the continuous flow column removal, the TiO₂/Al₂O₃ microspheres achieved sorption capacities of ∼31 mg g^-1 and ∼19 mg g^-1 until the breakthrough point for MO and RB, respectively. The findings reveal that TiO₂-modified Al₂O₃ microspheres were rapidly prepared by spray pyrolysis, and they effectively treated organic dyes in water in batch and continuous flow removal processes.

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

Congo Red Dye Adsorption using Magnesium Hydroxide from Seawater Bittern

The study of Mg(OH)2 from seawater bittern as an adsorbent for Congo red (CR) from an aqueous solution has been performed. This study aimed to determine the effect of pH, contact time, and initial CR concentration on CR adsorption by Mg(OH)2. The adsorption kinetics and isotherms of CR on Mg(OH)2 in an aqueous solution were also studied. The optimum adsorption was obtained at pH 8 within 90 minutes of contact time with an adsorption capacity of 46.3 mg/g for an initial CR concentration of 29 mg/L. The adsorption process followed the Freundlich isotherm model with an n value of 2.579 and the pseudo-second-order kinetic model with a k2 value of 0.0021 g mg−1min−1.

Microwave-assisted preparation of cotton stem-derived activated carbon for dye removal from synthetic wastewater

Cotton stem is used to produce the high-efficient adsorbent (CSA) for Rhodamine B (RB) dye removal from wastewater, and hydrogen rich fuel gas via on-pot method using microwave heating. The adsorption data indicate that RB adsorption behavior follows the Langmuir model with the maximum adsorption capacity of 265.96 mg/g, whereas the adsorption kinetics follows the pseudo-second-order model. Thermodynamic calculations indicate that RB adsorption on CSA is spontaneous and endothermic process. The adsorption data are fitted to the Thomas and Yoon-Nelson model to predict the breakthrough curve in the column experiment. The RB removal could still be maintained at 71.22% of the original value after five cycles, demonstrating the reusability of CSA. The chemical functional groups, electrostatic interaction, and pore filling of CSA are found to be responsible for high RB adsorption capability. CSA exhibits excellent RB removal efficiency in treating actual water. The major components of byproduct gases collected from activation process are H₂ and CO.

A Review of the Removal of Dyestuffs from Effluents onto Biochar

The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters.

Carboxylate-functionalized dragon fruit peel powder as an effective adsorbent for the removal of Rhodamine B (cationic dye) from aqueous solution: adsorption behavior and mechanism

In this study, we used a simple and low-toxicity chemical treatment to make a carboxylate-functionalized dragon fruit peel powder (CF-DFPP) from dragon fruit peel to improve its capacity for adsorbing Rhodamine B (RhB) from an aqueous medium. Field Emission-Scanning Electron Microscopy/Energy-Dispersive X-ray (FE-SEM/EDX), point of zero charges (pH_PZC), Brunauer-Emmett-Teller (BET), and Fourier Transform Infrared (FT-IR) analyses were performed to characterize the adsorbent materials. The adsorption performance and mechanism for the removal of RhB were examined. The kinetic, isotherm and thermodynamic parameters were employed to evaluate the adsorption mechanism. Compared to other models, the Langmuir isotherm and PSO kinetic models better defined the experimental data. CF-DFPP adsorbent exhibited a maximum adsorption efficiency of 228.7 mg/g at 298 K for RhB adsorption. Thermodynamic analysis revealed that the adsorption of RhB by CF-DFPP was spontaneous (ΔG^o < 0) and exothermic (ΔH^o < 0) nature of the process. Different eluting agents were used in desorption tests, and NaOH was revealed to have greater desorption efficiency (96.8%). Furthermore, regeneration examinations revealed that the biosorbent could effectively retain RhB, even after six adsorption/desorption cycles. These findings demonstrated that the CF-DFPP might be a novel material for removing RhB from an aqueous medium.

The Effect of Chemical Activating Agent on the Properties of Activated Carbon from Sago Waste

The effect of chemical activators on the properties of activated carbon from sago waste was conducted in this study by using ZnCl2, H3PO4, KOH, and KMnO4 chemical solutions. The carbonized sago waste was added to each chemical solution, boiled at 85 °C for 4 h, and heated at 600 °C for 3 h. The porosity, microstructural, proximate, and surface chemistry analyses were carried out using nitrogen adsorption with employing the Brunauer Emmett Teller (BET) method and the Barret-Joyner-Halenda (BJH) calculation, scanning electron microscopy by using energy dispersive spectroscopy, X-ray diffractometer, simultaneous thermogravimetric analysis system, and the Fourier-transform infrared spectroscopy. The results showed that the activated carbon prepared using ZnCl2 acid had the highest specific surface area of 546.61 m2/g, while the KOH activating agent surpassed other chemicals in terms of a refined structure and morphology, with the lowest ash content of 10.90%. The surface chemistry study revealed that ZnCl2 and KOH activated carbon showed phenol and carboxylate groups. Hence, ZnCl2 acid was suggested as activating agents for micropore carbon, while KOH was favorable to producing a mesopore-activated carbon from sago waste.

Evaluation of poly(ethylene diamine-trimesoyl chloride)-modified diatomite as efficient adsorbent for removal of rhodamine B from wastewater samples

Diatomite (D) as a low-cost and eco-friendly clay was modified by ethylene diamine (EDA)-trimesoyl chloride (TMC) polymer to achieve a novel adsorbent for efficient removal of rhodamine B dye (RB) from wastewater samples. The EDA-TMC polymer was grafted to the surface of diatomite by in situ interfacial polymerization. The prepared p(EDA-TMC)/D adsorbent was characterized by XRD, FTIR, and SEM/EDX techniques. The effective experimental parameters on the adsorption performance were optimized with factorial design analysis. The equilibrium data were better correlated by non-linear Langmuir model compared to non-linear Freundlich model. The Langmuir monolayer adsorption capacity of the p(EDA-TMC)/D adsorbent was determined as 371.8 mg g^-1. The key adsorption parameters were optimized by experimental design analysis. The kinetic findings showed the adsorption mechanism of RB onto p(EDA-TMC)/D adsorbent was well designated by the pseudo-second-order kinetic model. The thermodynamic results indicate that the RB adsorption had an exothermic character in thermal nature and was less favorable with increasing temperature from 20 to 60 °C. Furthermore, the adsorption/desorption yield of p(EDA-TMC)/D was still 80%/70% after 5^th cycle and reduced to 60%/52% at the end of 8^th cycle. Thus, the present study revealed that the developed p(EDA-TMC)/D composite had great adsorption potential for removal of RB from wastewater samples compared to that of different kinds of adsorbents reported in the literature.

Performance of activated carbons prepared from spent tyres in the adsorption of rhodamine B in aqueous solutions

Activated carbons were produced from spent tyre pyrolysis char by steam or CO₂ activation and evaluated for their performance in rhodamine B (RhB) adsorption in aqueous solutions. The effect of RhB starting concentration (80-150 mg L^-1), contact time (0-80 min), temperature (298-318 K) and initial pH on the adsorption process was examined. Pseudo-first-order and pseudo-second-order models were carried out to fit the experimental data to derive RhB adsorption kinetics. Langmuir, Freundlich and Temkin isotherm models were applied to depict RhB adsorption behaviour of the prepared activated carbons. Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were calculated. It has been found that the activated carbons can effectively adsorb RhB due to high mesoporosity and RhB equilibrium adsorption capacity (q_e) increased almost linearly with increasing total mesopore volumes, regardless of the activation agents. When BET surface areas are similar, CO₂-activated carbon obtained higher q_e than steam due to higher mesoporosity of CO₂-activated carbon. The results show that pseudo-second-order well fitted the experimental data. RhB starting concentration increased from 80 to 150 mg L^-1 causing q_e increased from 158 to 251 mg g^-1 but RhB removal decreased from 99.7 to 84.5%. The RhB adsorption process follows the Langmuir model and thermodynamic calculation, indicating RhB adsorption is an endothermic, spontaneous process, dominated by both chemisorption and physisorption.

Trapping Rhodamine B dye using functionalized mango (Mangifera indica) pod

The use of acid-modified mango pod (AMMP) sorbent for removing Rhodamine B (Rh-B) dye from aqueous media was investigated. Raw mango pod (RMP) and AMMP sorbents were characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), powdered X-ray diffractogram (PXRD), Fourier transform infrared (FTIR), point of zero charge pH (pH_pzc ), and Boehm titration (BT) techniques. Batch adsorption was employed to examine the influence of operational factors. Sorption kinetic parameters were calculated using pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The pseudo-second-order model best fitted the adsorption kinetic data most with maximum correlation coefficient (R²  > 0.99). The process of the adsorption was controlled by both boundary layer and intraparticle diffusion mechanisms. Four isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin) were utilized to analyze the equilibrium data at various temperatures. Freundlich model gave the best fit with the maximum regression (0.99), while the Langmuir isotherm model established a maximum monolayer adsorption capacity of 500 mg g^-1 . Thermodynamic parameters studied revealed that the interaction is spontaneous and endothermic in nature. The cost analysis of the current study provides convincing proof that AMMP is efficient for removing Rh-B dye from solution by providing a saving of 225.2 USD/kg, which is eight times cheaper than commercial activated carbon. Consequently, the study revealed that AMMP is a viable, effective, and sustainable sorbent for Rhodamine B dye removal. PRACTITIONER POINTS: The powdered X-ray diffractogram (PXRD) showed the formation of new and intense peaks with the presence of highly organized crystalline structures on acid-modified mango pod (AMMP). Surface morphology of AMMP showed well-developed open surface pores required for effective adsorption of Rh B dye molecules. Economic feasibility of the present study showed that AMMP is more affordable than commercial activated carbon that costs USD 259.5/kg, thus translated to a saving cost of USD 225.2/kg and more than 7.5 times cheaper than the commercial activated carbon (CAC).

Synthesis of glass fiber sphere using waste printed circuit board to support MIL-100(Fe) for dye adsorption in water

Glass fiber sphere (GFS), used as support of MIL-100(Fe) to treat dye wastewater, was successfully synthesized using glass fibers from waste printed circuit board. Structural and textural features of MIL-100(Fe) supported by GFS (GFS/MIL-100(Fe)) were characterized by different techniques. GFS/MIL-100(Fe) showed higher specific surface area and better rhodamine B (RHB) removal performance as well as reusability. RHB removal percentage by GFS/MIL-100(Fe) reached 92% in 11 h, compared with 79% in 7 h of MIL-100(Fe). The highest RHB removal rate was obtained with the GFS/MIL-100(Fe) concentration of 20 g/L. Increasing RHB concentration over 100 mg/L reduced the time needed for saturated adsorption from 11 to 7 h. The best RHB removal performance of GFS/MIL-100(Fe) was obtained at pH = 3, and the removal percentage was almost the same in the pH range 5-11. The adsorption data fitted the pseudo-second-order kinetics better than the pseudo-first-order kinetics, and the adsorption isotherm data fitted Langmuir model better than Freundlich model. MIL-100(Fe) synthesized in organic solvents showed higher loading rate than that obtained in water. GFS/MIL-100(Fe) also showed promising removal performances for methylene blue, acid orange 7, and malachite green in water. The removal percentage of RHB was still 80% even after being used for 3 times. The results of this study indicate the prospect of synthesizing GFS with glass fibers from waste printed circuit boards and its use as the support of MIL-100(Fe).

Efficiency of Wood-Dust of Dalbergia sisoo as Low-Cost Adsorbent for Rhodamine-B Dye Removal

Wood-dust of Dalbergia sisoo (Sisau) derived activated carbon (AC) was successfully tested as an adsorbent material for the removal of rhodamine B dye from an aqueous solution. The AC was prepared in a laboratory by the carbonization of wood powder of Dalbergia sisoo at 400 °C in an inert atmosphere of N₂, which was chemically activated with H₃PO₄. Several instrumental techniques have been employed to characterize the as-prepared AC (Db-s). Thermogravimetric analysis (TGA)/differential scanning colorimetry (DSC) confirmed that 400 °C was an appropriate temperature for the carbonization of raw wood powder. The FTIR spectra clearly confirmed the presence of oxygenated functional groups such as hydroxyl (–OH), aldehyde/ketone (–CHO/C=O) and ether (C–O–C) at its surface. The XRD pattern showed the amorphous structure of carbon having the 002 and 100 planes, whereas the Raman spectra clearly displayed G and D bands that further confirmed the amorphous nature of carbon. The SEM images displayed the high porosity, and the BET analysis revealed a high surface area of 1376 m² g⁻¹, a pore volume of 1.2 cm³ g⁻¹, and a pore size of 4.06 nm with the coexistence of micropores and mesopores. The adsorption of dyes was performed by varying the dye concentration, pH, time, and the sample dose. The maximum percent of RhB dye removal by AC (Db-s) was 98.4% at an aqueous solution of 20 ppm, pH 8.5, an adsorbent dose of 0.03 g, and a time of 5 min. This study proved to be successful in addressing the local problem of wastewater pollution of garment and textile industrial effluents using locally available agro-waste of Dalbergia sisoo.

PEG/Sodium Tripolyphosphate-Modified Chitosan/Activated Carbon Membrane for Rhodamine B Removal

Textile dyes from wastewater effluent are highly toxic to both living species and aqueous environments. An environmentally friendly method to remove hazardous dyes from wastewater in the textile industry has been a challenge. Chitosan (CS) and activated carbon (AC) are widely used as adsorbents for dye removal. However, the poor porosity and unsatisfactory stability of CS and the unfriendly cost of AC limited their applications to be used alone as a single adsorbent. Here, we report a novel method to prepare a CS/AC membrane using PEG10000 as a porogen and sodium tripolyphosphate (TPP) as a cross-linking agent. The adsorption efficiency and reusability of the PEG/TPP-modified CS/AC membrane to remove RhB were investigated based on dynamic and static adsorption models. The results reveal that the adsorption performance of CS/AC membranes was significantly improved after the PEG/TPP modification based on the abundance macroporous structure. The modified CS/AC membrane with a 30% AC doping ratio exhibited an excellent adsorption efficiency of 91.29 and 73.91% in the dynamic and static adsorption processes, respectively. These results provide new insights into designing membranes to remove dyes from wastewater efficiently.

Carnauba (Copernicia prunifera) palm tree biomass as adsorbent for Pb(II) and Cd(II) from water medium

Plant-based biomass (CFB (carnauba fruit biomass)) obtained from the fruit exocarp of the species Copernicia prunifera (Mill.) H.E. Moore (carnauba) was evaluated for its viability as an adsorbent of potentially toxic metals in aqueous medium. The CFB was characterized by powder X-ray spectroscopy (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential to investigate the morphology of the biosorbent and its interaction with water soluble metal ions of Pb and Cd. The biomass presents an amorphous structure, with negative zeta potential (- 2.59 mV), and the presence of functional groups such as O-H, C-O-C, C-H, and C=O. The removal potential of Pb(II) and Cd(II) was performed in a batch system, and monoelement solutions were tested to assess the effects of adsorbent dose and initial metal ion concentration, pH at the point of zero charge (pH_PZC), sorption kinetics, and adsorption capacity. The most appropriate adsorbent concentration was 5 g/L, and sorption studies were carried out at pH 5.0 (pH_PZC = 4.68), in which the surface of the adsorbent shows negative charges and favors the adsorption of metal ions. Kinetic studies showed that the pseudo-second order model best fit the experimental data, and equilibrium was reached at 120 min of contact time. The experimental sorption capacity (SC_exp) for Pb and Cd was around 28 and 34 mg/g, respectively, and six different non-linear isotherm models were used to describe the sorption phenomena, among them, four with 2 parameters, i.e., Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (DR), respectively, and two with 3 parameters, namely, SIPS and Hill. The non-linear Temkin and Freundlich isotherm models best fit the experimental data for Pb(II) and Cd(II), respectively. According to the Langmuir model, Q_max was 26 mg/g and 58 mg/g for Pb(II) and Cd(II), respectively, indicating the efficiency of CFB as a new alternative to conventional methods for the removal of potentially toxic metals from aqueous medium.

Bio-mass derived functionalized graphene aerogel: a sustainable approach for the removal of multiple organic dyes and their mixtures

Herein, fabrication of a functionalized graphene aerogel (f-GA) from a biomass (pear fruit)-derived graphene aerogel (GA) is described. f-GA is showing better adsorption capacity towards CV, MB and RhB dyes than GA and activated charcoal.

Adsorptive Removal of Rhodamine B Using Novel Adsorbent-Based Surfactant-Modified Alpha Alumina Nanoparticles

The objective of the present study is to investigate removal of cationic dye, rhodamine B (RhB), in water environment using a high-performance absorbent based on metal oxide nanomaterials toward green chemistry. The adsorption of sodium dodecyl sulfate (SDS) onto synthesized alpha alumina (α-Al₂O₃) material (M0) at different ionic strengths under low pH was studied to fabricate a new adsorbent as SDS-modified α-Al₂O₃ material (M1). The RhB removal using M1 was much higher than M0 under the same experimental conditions. The optimal conditions for RhB removal using M1 were found to be contact time 30 min, pH 4, and adsorbent dosage 5 mg/mL. The maximum RhB removal using M1 achieved 100%, and adsorption amount reached 52.0 mg/g. Adsorption isotherms of RhB onto M1 were well fitted by the two-step adsorption model. The electrostatic attraction between positive RhB molecules and negatively charged M1 surface controlled the adsorption that was evaluated by the surface charge change with zeta potential and adsorption isotherms. Very high RhB removal of greater than 98% after four regenerations of M1 and the maximum removal for all actual textile wastewater samples demonstrate that SDS-modified nano α-Al₂O₃ is a high-performance and reusable material for RhB removal from wastewater.

The states of water in tryptophan grafted hydroxypropyl methylcellulose hydrogels and their effect on the adsorption of methylene blue and rhodamine B

Tryptophan (Trp) decorated hydroxypropyl methylcellulose (HPMC) cryogels were prepared by a one-step reaction with citric acid. The increase of Trp content in the 3D network from 0 to 2.18 wt% increased the apparent density from 0.0267 g.cm^-3 to 0.0381 g.cm^-3 and the compression modulus from 94 kPa to 201 kPa, due to hydrophobic interactions between Trp molecules. The increase of Trp content in HPMC-Trp hydrogels increased the amount of non-freezing water, estimated from differential scanning calorimetry, and the amount of freezing water, which was determined by time-domain nuclear magnetic resonance. The adsorption capacity of methylene blue (MB) and rhodamine B (RB) on HPMC-Trp hydrogels increased with Trp content and the amount of freezing water. HPMC-Trp hydrogels could be recycled 6 times keeping the original adsorptive capacity. The diffusional constants of MB and RB tended to increase with Trp content. RB adsorbed on HPMC-Trp hydrogels presented a bathochromic shift of fluorescence.

Biomass-Derived Activated Carbon as a Catalyst for the Effective Degradation of Rhodamine B dye

Activated carbon (AC) was fabricated from carrot waste using ZnCl2 as the activating agent and calcined at 700 °C for 2 h in a tube furnace. The as-synthesized AC was characterized using Fourier-transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis; the results revealed that it exhibited a high specific surface area and high porosity. Moreover, this material displayed superior catalytic activity for the degradation of toxic Rhodamine B (RhB) dye. Rate constant for the degradation of RhB was ascertained at different experimental conditions. Lastly, we used the Arrhenius equation and determined that the activation energy for the decomposition of RhB using AC was approximately 35.9 kJ mol−1, which was very low. Hopefully it will create a great platform for the degradation of other toxic dye in near future.

Fabrication of N-doped carbons from waste bamboo shoot shell with high removal efficiency of organic dyes from water

N-doped carbons were obtained from bamboo shoot shell via hydrothermal pretreatment under salt assistance followed by carbonization, using melamine as nitrogen source. The carbons with tubular morphology and surface areas in 406-489 m²/g range were used as adsorbents for the removal of methyl orange (MO) and rhodamine B (RhB). Adsorption isotherms and kinetic fitting showed much better accordance with Freundlich model and pseudo-second-order, showing balanced capacity (q_e) of 50 mg/g for MO and 42 mg/g for RhB on the pristine carbons (BHC-800) at 25 °C. After N-doping treatment, carbons (BSC-M20) had q_e of MO and RhB up to 140 and 100 mg/g, respectively, confirming a positive effect of N-doping on the enhancement of dyes removal. The findings indicated that hydrothermal treatment followed by carbonization was efficient to obtain N-doped carbons from biomass materials, and the present BSS-derived carbons were promising adsorbents for organic dyes removal from water.

Biodegradation and adsorption of micropollutants by biological activated carbon from a drinking water production plant

The presence of micropollutants in surface water is a potential threat for the production of high quality and safe drinking water. Adsorption of micropollutants onto granular activated carbon (GAC) in fixed-bed filters is often applied as a polishing step in the production of drinking water. Activated carbon can act as a carrier material for biofilm, hence biodegradation can be an additional removal mechanism for micropollutants in GAC filters. To assess the potential of biofilm to biodegrade micropollutants, it is necessary to distinguish adsorption from biodegradation as a removal mechanism. We performed experiments at 5 °C and 20 °C with biologically active and autoclaved GAC to assess the biodegradation of micropollutants by the biofilm grown on the GAC surface. Ten micropollutants were selected as model compounds. Three of them, iopromide, iopamidol and metformin, were biodegraded by the GAC biofilm. Additionally, we observed that temperature can increase or decrease adsorption, depending on the micropollutant studied. Finally, we compared the adsorption capacity of GAC used for more than 100,000 bed volumes and fresh GAC. We demonstrated that used GAC shows a higher adsorption capacity for guanylurea, metformin and hexamethylenetetramine and only a limited reduction in adsorption capacity for diclofenac and benzotriazole compared to fresh GAC.

Rhodamine B dye sequestration using Gmelina aborea leaf powder

Chemically prepared activated carbon derived from Gmelina aborea leaves (GALAC) were used as adsorbent for the removal of Rhodamine B (Rh-B) dye from aqueous solutions. The adsorptive characteristics of activated carbon (AC) prepared from Gmelina aborea leaves (GAL) were studied using SEM, FTIR, pH point of zero charge (pHpzc) and Boehm Titration (BT) techniques respectively. The effects of pH, contact time, initial dye concentration and solution temperature were also examined. Experimental data were analyzed using four different isotherm models: Langmuir, Freundlich, Temkin and Dubinin-Radushkevich. Four adsorption kinetic models: Pseudo-first-order (PFO), Pseudo-second-order (PSO), Elovich and Intraparticle diffusion models to establish the kinetics of adsorption process. The RhB dye adsorption on GALAC was best described by Langmuir isotherm model with maximum monolayer coverage of 1000 mg g-1 and R2 value of 0. 9999. The EDX analysis revealed that GALAC contained 82.81% by weight and 91.2% by atom of carbon contents which are requisites for high adsorption capacity. Adsorption kinetic data best fitted the PSO kinetic model. Thermodynamic parameters obtained for GALAC are (ΔGo ranged from -22.71 to -18.19 kJmol-1; ΔHo: 1.51 kJmol-1; and ΔSo: 0.39 kJmol-1 K-1respectively) indicating that the RhB dye removal from aqueous solutions by GALAC was spontaneous and endothermic in nature. The cost analysis established that GALAC is approximately eleven times cheaper than CAC thereby providing a saving of 351.41USD/kg. Chemically treated GAL was found to be an effective absorbent for the removal of RhB dye from aqueous solution.

Synthesis of Chitosan-Ignosulfonate Composite as an Adsorbent for Dyes and Metal Ions Removal from Wastewater

Sodium lignosulfonate is a polymer with extensive sources and abundant functional groups. Therefore, it has potential value for research and wide utilization. In this study, the adsorption material was prepared by blending sodium lignosulfonate and chitosan, which could adsorb anionic and cationic dyes and metal ions. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetry (TG). The results showed that the composite was cross-linked mainly by the strong electrostatic interaction between the protonated amino group in chitosan and the sulfonate group in sodium lignosulfonate. Moreover, the effects of initial concentration, adsorption time, initial pH, and mass ratio of chitosan to sodium lignosulfonate on the adsorption performance of the composite were investigated. Meanwhile, the adsorption processes were agreed well with the pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption mechanism was that the electrostatic interaction between the protonated amino and hydroxyl groups of the composite with anionic (SO3 -) and HCrO4 - groups of Congo red and Cr(VI), respectively. In addition, the electrostatic interaction between SO3 - of the composite and positively charged group of Rhodamine B played an important role in the adsorption of Rhodamine B.

Parabens Adsorption onto Activated Carbon: Relation with Chemical and Structural Properties

Parabens (alkyl-p-hidroxybenzoates) are antimicrobial preservatives used in personal care products, classified as an endocrine disruptor, so they are considered emerging contaminants. A raw version of activated carbons obtained from African palm shell (Elaeis guineensis) modified chemically by impregnation with salts of CaCl₂ (GC2), MgCl₂ (GM2) and Cu(NO₃)₂ (GCu2) at 2% wt/v and carbonized in CO₂ atmosphere at 1173 K was prepared. The process of adsorption of methyl (MePB) and ethylparaben (EtPB) from aqueous solution on the activated carbons at 18 °C was studied and related to the interactions between the adsorbate and the adsorbent, which can be quantified through the determination of immersion enthalpies in aqueous solutions of corresponding paraben, showing the lowest-value carbon GM2, which has a surface area of 608 m² × g^-1, while the highest values correspond to the activated carbon GCu2, with a surface area of 896 m² × g^-1 and the highest content of surface acid sites (0.42 mmol × g^-1), such as lactonic and phenolic compounds, which indicates that the adsorbate-adsorbent interactions are favored by the presence of these, with interaction enthalpies that vary between 5.72 and 51.95 J × g^-1 for MePB adsorption and 1.24 and 52.38 J × g^-1 for EtPB adsorption showing that the process is endothermic.

Removal of Phenol from Steel Plant Wastewater in Three Dimensional Electrochemical (TDE) Process using CoFe2O4@AC/H2O2

This study investigated the removal of phenol from steel industry wastewater by three dimensional electrochemical (TDE) process using CoFe2O4 nanobiocomposite based activated carbon in the presence of H2O2 (EC-CoFe2O4@AC-H2O2). In this study, CoFe2O4 nanobiocomposite-foundation activated carbon (CoFe2O4@AC) was used as microelectrode, adsorbent, and activator for peroxide hydrogen. The removal efficiency of phenol and COD was investigated through the parameters of pH, contact time, CoFe2O4@AC dosage, current density, and H2O2 concentration. The highest removal rates of phenol and COD were >99% and 98%, respectively. Also, steel plant wastewater under the optimal conditions of pH = 6.5, current density = 15 mA cm−2, contact time = 25 min, H2O2 concentration of 1.0 mM, and CoFe2O4@AC dose = 0.3 g L−1. Kinetic analysis revealed that the adsorption experimental data was best fitted by the pseudo-first-order model.

H3PO4-activated carbons produced from açai stones and Brazil nut shells: removal of basic blue 26 dye from aqueous solutions by adsorption

The adsorption characteristics of C.I. basic blue 26 (BB26) from aqueous solutions onto H₃PO₄-activated carbons (ACs) produced from açai stones (Euterpe oleracea Martius) and Brazil nut shells (Bertholletia excelsa H. B. K) were investigated in a batch system. The ACs were characterized by XRD, FT-IR, N₂ adsorption at 77 K, mercury porosimetry, and acidity/basicity analysis. The pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model were used for the kinetic interpretations. The adsorption processes follow the pseudo-second-order kinetic model. The Boyd plots revealed that the adsorption processes were mainly controlled by film diffusion. Equilibrium data were analyzed by the Langmuir and Freundlich models, at different temperatures. The equilibrium data were best represented by the Langmuir isotherm. The adsorption processes were found to be favorable, exothermic, and spontaneous. The açai stones and Brazil nut shells-based ACs were shown to be effective adsorbents for removal of BB26 from aqueous solutions.

Photocatalytic Performance of NiO/NiTiO3 Composite Nanofiber Films

Photocatalytic degradation of pollutants is one of the cleanest technologies for environmental remediation. Herein, we prepared NiO/NiTiO3 heterostructure nanofiber (200 nm) films by electrospinning and high temperature heat treatment, using nickel acetate and tetrabutyltitanate as nickel and titanium sources, respectively. The NiO/NiTiO3 heterostructure has advantages of good photodegradation rate constant and stability. By controlling the temperature, we can optimize the phase composition of these nanofibers for better photocatalytic performance. Based on our findings of the Rhodamine B degradation results, the best performance was obtained with 10% NiO and 90% NiTiO3; 92.9% of the Rhodamine B (5 mg/L) was degraded after reaction under full spectrum irradiation for 60 min. More importantly, the repeating test showed that these nanofiber films can remain active and stable after multiple cycles. The mechanisms of the photocatalysis reactions were also discussed. This demonstration provides a guideline in designing a new photocatalyst that we hope will serve the environmental needs for this and the coming century.

Efficient removal of dyes from dyeing wastewater by powder activated charcoal/titanate nanotube nanocomposites: adsorption and photoregeneration

Effective removal of dyes has been widely investigated by the adsorption of powder activated carbon and photodegradation by titanate nanotubes (TNTs). In this study, a facile one-step alkaline-hydrothermal method was applied to synthesize powder activated charcoal-supported TNTs (TNTs@PAC). Adsorption of three representative dyes, i.e., cationic methylene blue (MB), cationic rhodamine B (RhB), and anionic methyl orange (MO), onto TNTs@PAC was evaluated by the adsorption kinetic experiments and adsorption isotherms. The first 30 min is the main time phase of adsorption, and MB, RhB, and MO obtained the experimental equilibrium uptake of 173.30, 115.06, and 106.85 mg/g, respectively, indicating their final removal efficiencies of 100%, 69.36%, and 64.11%, respectively. The increase of pH value reduced adsorption capacity of MO (from 149.35 mg/g at pH of 2 to 96.99 mg/g at pH of 10), but facilitated MB adsorption, which was attributed to the charge distribution on the surface of TNTs@PAC and the charge of dyes at different pH. Furthermore, good capacity recoveries of MB by TNTs@PAC (> 99%) were observed after UV irradiation treatment, indicating the used TNTs@PAC can be easily recycled for the adsorption of MB by UV irradiation. Overall, TNTs@PAC is an effective process for remediation of dye-contaminated water because of its adsorption performance for all selected dyes and good regeneration capacity for MB.

Removal of Rhodamine B (A Basic Dye) and Acid Yellow 17 (An Acidic Dye) from Aqueous Solutions by Ordered Mesoporous Carbon and Commercial Activated Carbon

In this work, adsorption of rhodamine B (RB) and acid yellow 17 (AY17) was investigated on ordered mesoporous carbon material obtained by soft-templating method with hydrochloric acid (ST-A). For comparison, the adsorption process on commercial activated carbon CWZ-22 was also carried out. The sorbents were characterized by nitrogen adsorption/desorption isotherms and scanning electron microscopy. Langmuir and Freundlich adsorption isotherm models were applied to simulate the equilibrium data of RB and AY17. Adsorption isotherm data could be better described by the Langmuir model than the Freundlich model. The adsorption kinetics of RB and AY17 on studied carbons could be well depicted by using pseudo-second-order kinetic modeling. The adsorption capacity increased with temperature increase in the range of 298–315 K. In the whole diffusion process, the intraparticle diffusion was involved, but not the whole rate-controlling step. The calculated thermodynamic parameters, including Gibbs free energy (∆G), enthalpy (∆H), and entropy (ΔS) suggested that adsorption processes of RB and AY17 on ST-A and CWZ-22 were endothermic and spontaneous.

N-Doped Carbon Aerogels Obtained from APMP Fiber Aerogels Saturated with Rhodamine Dye and Their Application as Supercapacitor Electrodes

We developed an efficient and environmentally friendly strategy for synthesizing an N-doped carbon aerogel by the carbonization of an alkaline peroxide mechanical pulp (APMP) fiber aerogel saturated with rhodamine B (RB) dyes. The APMP aerogel was prepared via cellulose extraction, sol-gel, and freeze drying. The resulting aerogel had a high adsorption capacity (250 mg g−1) and a fast adsorption rate (within 30 s) towards RB dyes. The saturated aerogel was used as a starting material for further carbonization to prepare N-doped carbon aerogels. SEM studies showed that the 3D network structure of the APMP aerogels was well preserved after RB adsorption and carbonization. The prepared carbon aerogel exhibited a graphitized structure, and N (2.15%) was doped at pyridinic N and pyrrolic N sites in the 3D carbon network. The specific capacitance of the N-doped carbon aerogel reached 185 F g−1 at a current density of 1 A g−1, which is higher than carbon aerogels (155 F g−1).