Corncob-derived activated carbon for roxarsone removal from aqueous solution: isotherms, kinetics, and mechanism

Efficient roxarsone degradation by low-dose peroxymonosulfate with the activation of recycling iron-base composite material: Critical role of electron transfer

Pollutant degradation via electron transfer based on advanced oxidation processes (AOPs) provides an economical and energy-efficient method for pollution control. In this study, an iron-rich waste, heating pad waste (HPW), was recycled as a raw material, and a strong magnetic catalyst (Fe-HPW) was synthesized at high temperature (900 °C). Results showed that in the constructed Fe-HPW/PMS system, effective roxarsone (ROX) degradation and TOC removal (72.54%) were achieved at a low-dose of oxidant (PMS, 0.05 mM) and catalyst (Fe-HPW, 0.05 g L-1), the ratio of PMS to ROX was only 2.5:1. In addition, the released inorganic arsenic was effectively removed from the solution. The analysis of the experimental results showed that ROX was effectively degraded by forming PMS/catalyst surface complexes (Fe-HPW-PMS*) to mediate electron transfer in the Fe-HPW/PMS system. Besides, this system performed effective ROX degradation over a wide pH range (pH=3-9) and showed high resistance to different water parameters. Overall, this study not only provides a new direction for the recycling application of HPW but also re-emphasizes the neglected nonradical pathway in advanced oxidation processes.

3D-Printed MOFs/Polymer Composite as a Separatable Adsorbent for the Removal of Phenylarsenic Acid in the Aqueous Solution

Metal-organic frameworks (MOFs) are emerging as advanced nanoporous materials to remove phenylarsenic acid, p-arsanilic acid (p-ASA), and roxarsone (ROX) in the aqueous solution, while MOFs are often present as powder state and encounter difficulties in recovery after adsorption, which greatly limit their practical application in the aqueous environments. Herein, MIL-101 (Fe), a typical MOF, was mixed with sodium alginate and gelatin to prepare MIL-101@CAGE by three-dimensional (3D) printing technology, which was then used as a separatable adsorbent to remove phenylarsenic acid in the aqueous solution. The structure of 3D-printed MIL-101@CAGE was first characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetry and differential thermogravimetry (TG-DTG). The octahedral morphology of MIL-101 (Fe) was found unchanged during the 3D printing process. Then, the adsorption process of MIL-101@CAGE on phenylarsenic acids was systematically investigated by adsorption kinetics, adsorption isotherms, adsorption thermodynamics, condition experiments, and cyclic regeneration experiments. Finally, the adsorption mechanism between MIL-101@CAGE and phenylarsenic acid was further investigated. The results showed that the Langmuir, Freundlich, and Temkin isotherms were well fit, and according to the Langmuir fitting results, the maximum adsorption amounts of MIL-101@CAGE on p-ASA and ROX at 25 °C were 106.98 and 120.28 mg/g, respectively. The removal of p-ASA and ROX by MIL-101@CAGE remained stable over a wide pH range and in the presence of various coexisting ions. The regeneration experiments showed that the 3D-printed MIL-101@CAGE could still maintain a more than 90% removal rate after five cycles. The adsorption mechanism of this system might include π-π stacking interactions between the benzene ring on the phenylarsenic acids and the organic ligands in MIL-101@CAGE, hydrogen-bonding, and ligand-bonding interactions (Fe-O-As). This study provides a new idea for the scale preparation of a separatable and recyclable adsorbent based on MOF material for the efficient removal of phenylarsenic acid in the aqueous solution.

MoS2 nanobelts-carbon hybrid material for supercapacitor applications

The MoS2 nanobelts/Carbon hybrid nanostructure was synthesized by the simple hydrothermal method. The MoS2 nanobelts were distributed in the interlayers of Lemon grass-derived carbon (LG-C), provides the active sites and avoid restacking of the sheets. The structural and morphological characterization of MoS2/LG-C and LG-C were performed by Raman spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical measurements were studied with cyclic voltammetry, the galvanostatic charge-discharge method, and electrochemical impedance spectroscopy. The specific capacitance of MoS2/LG-C and LG-C exhibits 77.5 F g-1 and 30.1 F g-1 at a current density of 0.5 A g-1. The MoS2/LG-C-based supercapacitor provided the maximum power density and energy density of 273.2 W kg-1 and 2.1 Wh kg-1, respectively. Furthermore, the cyclic stability of MoS2/LG-C was tested using charging-discharging up to 3,000 cycles, confirming only a 71.6% capacitance retention at a current density of 3 A g-1. The result showed that MoS2/LG-C is a superior low-cost electrode material that delivered a high electrochemical performance for the next generation of electrochemical energy storage.

Insights into the mechanically resilient, well-balanced polymeric membranes by incorporating Rhizophora mucronata derived activated carbon for sustainable wastewater decontamination

In this study, hydrophilic activated carbon has been prepared and used to synthesize innovative activated carbon/polysulfone mixed matrix membranes (MMMs). These membranes were investigated in terms of membrane morphology, hydrophilicity, antifouling ability, and metal ions rejection. The activated carbon (AC) was prepared from a simple chemical activation method using Rhizophora mucronata propagules, which are rich in aerenchyma cells and possess a high surface area. The hydrophilicity of the MMMs is enhanced by the incorporation of activated carbon, which is confirmed by the measurement of equilibrium water contact angle, water uptake and pure water flux. The optimized concentration of 0.625 wt% activated carbon (A₂) incorporated mixed matrix membrane exhibits better rejection efficiencies of 98 ± 0.5%, 99 ± 0.5%, 92 ± 2%, and 44 ± 1% for Pb⁺², Cd⁺², Hg⁺², and F^- with the permeate flux of 28.27, 31.88, 33.21, 43.82 L/m²/h, respectively. The fabricated mixed matrix membranes demonstrated an excellent flux recovery ratio and reversible fouling, when filtrating a mixed feed solution containing 200 ppm BSA, 10 ppm Pb⁺² and 10 ppm Cd⁺². The optimized A₂ membrane showed excellent long-term stability up to 120 h without compromising in permeate flux and rejection efficiency. Finally, a numerical investigation using a usual transport model has shown that dielectric exclusion was the most probable mechanism that can physically explain experimental trends.

Salt sealing induced in situ N-doped porous carbon derived from wheat bran for the removal of doxycycline from aqueous solution

In situ N-doped porous carbon (NPC) derived from wheat bran via a convenient salt sealing and air-assisted strategy was prepared for the removal of doxycycline (DOX) from aqueous solution. The NPC was precisely characterized by SEM, FTIR, XPS and BET analysis. Additionally, the experimental variables including contact time, adsorbent dosage of NPC and pH were optimized by using Box-Behnken design (BBD) under response surface methodology (RSM). The predicted adsorption capacity of DOX was found to be 291.14 mg g-1 under optimalizing experimental conditions of 196 min contact time, 0.2 g L-1 adsorbent dosage and pH 5.78. The adsorption experimental data fitted Langmuir, Koble-Corrigan and Redlich-Peterson models well, and the pseudo-second-order model perfectly described the DOX adsorption process onto NPC. Thermodynamic parameters of DOX adsorbed onto NPC indicated that the adsorption process was spontaneous and endothermic. Moreover, the adsorption of DOX on NPC was mostly controlled by electrostatic interaction, π-π electron-donator-acceptor (EDA) interaction, hydrogen-bonding and Lewis acid-base effect. Besides, the N element of NPC also played a role in capturing DOX. The maximum monolayer adsorption capacity of DOX was turn out to be 333.23 mg g-1 at 298 K, which suggested that the NPC could be a prospectively adsorbent for the removal of DOX from wastewater.

Nanocomposites of immobilized nano-zirconia on low-cost activated carbon derived from hazelnut shell for enhanced removal of 3-Nitro-4-Hydroxy-Phenylarsonic acid from water

3-Nitro-4-hydroxy-phenylarsonic acid (NHPA) as a veterinary drug can degraded into highly toxic inorganic arsenic and will be harmful to environment and food safety. Nanocomposites for the uptake of NHPA were obtained by efficiently immobilizing the nano-sized zirconium oxide onto hazelnut shell-based activated carbon using pyrolysis method. We found that the pyrolysis temperature played a crucial role in the adsorptive performances of the nanocomposites. The prepared nanocomposite at pyrolysis temperature of 600 °C with a mass ratio of ZrOCl₂/activated carbon of 1:3 exhibited a fast adsorption equilibrium for NHPA within 5 min, excellent adsorption capacity of 825.7 mg g^-1 and the higher adsorption capacity with the increase in temperature from 20 to 45 °C across a pH range of 4-6. 90% of the NHPA uptake was sustained in the NaNO₃ solution of 0.7 mol L^-1. The adsorption data were well simulated by the Langmuir and pseudo-second order equations. Thermodynamic parameters suggested that the uptake of the NHPA occurred spontaneously (ΔG⁰<0) with an endothermic characteristic (ΔH⁰>0). A synergetic effect of electrostatic attraction, As-O-Zr surface coordination and π-π interaction is the main adsorption mechanism of the nanocomposites for the removal of the NHPA.

Electrochemical Sensing of Roxarsone on Natural Biomass-Derived Two-Dimensional Carbon Material as Promising Electrode Material

Herein, we report the electrochemical detection of roxarsone (ROX) on a two-dimensional (2D) activated carbon (AC)-modified glassy carbon electrode (GCE). Meso/microporous 2D-AC is synthesized from a natural biomass Desmostachya bipinnata, commonly known as Kusha in India. This environment-friendly material is synthesized by chemical activation using potassium hydroxide (KOH) and used as a sensitive electrochemical platform for the determination of ROX. It is an arsenic-based medicine, also used as a coccidiostat drug. It is widely used in poultry production as a feed additive to increase weight gain and improve feed efficiency. Long-term exposure to arsenic leads to serious health problems in humans and demands an urgent call for sensitive detection of ROX. Therefore, the green synthesis of 2D-AC is introduced as new carbon support for the electrochemical sensing of ROX. It provides a large surface area and efficiently supports enhanced electron transfer. Its electrocatalytic activity is seen in potassium ferri/ferrocyanide by cyclic voltammetry, where the 2D-AC-modified GCE delivered five to six times higher electrochemical performance as compared to the unmodified GCE. Electrochemical impedance spectroscopy is also performed to show that the prepared material has faster electron transfer and permits a diffusion-controlled process. It works well in real samples and also on disposable screen-printed carbon electrodes, thereby showing great potential for its application in clinical diagnosis. Our results exemplify a modest and innovative style for the synthesis of excellent electrode material in the electrochemical sensing platform and thus offer an inexpensive and highly sensitive novel approach for the electrochemical sensing of ROX and other similar drugs.

Biomass-derived versatile activated carbon removes both heavy metals and dye molecules from wastewater with near-unity efficiency: Mechanism and kinetics

Due to the ever-increasing industrialization, it is critical to protect the environment and conserve water resources by developing efficient wastewater treatment methods. Traditional methods that simultaneously remove heavy metal ions and complex dyes are too expensive and tedious to commercialize. This work demonstrates the versatility, effectiveness, and potential of a biomass-derived adsorbent (from a mangrove fruit of Rhizophora mucronata) synthesized using a simple route for rapid adsorption of complex dyes and heavy metals with an efficiency of near unity. The cartridges were prepared using activated carbon that removes both dye molecules and heavy metal ions simultaneously from wastewater, corroborating its applicability/feasibility to treat wastewater. Owing to the high surface area (1061.5 m²g^-1) and the pore volume (0.5325 cm³g^-1), the adsorbent showed >99% removal efficiency in just 12 min of exposure to wastewater. The cartridge exhibits >90% removal efficiency of both dyes and heavy metals from its mixed feed solution. The Langmuir and Freundlich models successfully explained the adsorption kinetics. These developed cartridges are versatile, rapid, efficient, and promising candidates for environmental remediation.

Nanocomposites of graphene and zirconia for adsorption of organic-arsenic drugs: Performances comparison and analysis of adsorption behavior

3-Nitro-4-hydroxy-phenylarsonic acid (3-NHPAA), an organic-arsenic compound, as one of widely used antibacterial veterinary drug, has greatly attracted the attention due to its potential threats on ecological environment. A series of the nanocomposites of zirconia nanoparticles with crystal phases (pure monoclinic, pure tetragonal and mixed phase (monoclinic + tetragonal)) anchored on reduced graphene oxide were produced through managing the concentration of triethanolamine solution and the reaction time. The effects of the crystal phases of the zirconia in the structure of the nanocomposites were played a key role in the adsorption performances of the 3-NHPAA. Experiment data identified the nanocomposites with monoclinic phase of zirconia excelled at the adsorption of the 3-NHPAA with a higher adsorption capacity up to 207.2 mg g^-1. The uptake of the 3-NHPAA by the three nanocomposites was implemented within 60 min and highly pH-dependent which illustrated electrostatic attraction between them as a main mechanism during the adsorption process. A wider pH range (3.8-8.8) for the uptake of the 3-NHPAA by the nanocomposites with the monoclinic phase of zirconia was obtained compared with the nanocomposites containing tetragonal phase (3.8-5.9) or the mixed phase (3.8-7.1) of zirconia. The adsorption of the 3-NHPAA was well described by the pseudo-second order kinetic and Langmuir equations. The thermodynamic parameters suggested that the adsorption of the 3-NHPAA over the three nanocomposites was endothermic and spontaneous in nature. In summary, the nanocomposites of reduced graphene oxide and monoclinic phase of zirconia nanoparticles as an adsorbent were better to the adsorption of the 3-NHPAA.

Current State of Porous Carbon for Wastewater Treatment

Porous materials constitute an attractive research field due to their high specific surfaces; high chemical stabilities; abundant pores; special electrical, optical, thermal, and mechanical properties; and their often higher reactivities. These materials are currently generating a great deal of enthusiasm, and they have been used in large and diverse applications, such as those relating to sensors and biosensors, catalysis and biocatalysis, separation and purification techniques, acoustic and electrical insulation, transport gas or charged species, drug delivery, and electrochemistry. Porous carbons are an important class of porous materials that have grown rapidly in recent years. They have the advantages of a tunable pore structure, good physical and chemical stability, a variable specific surface, and the possibility of easy functionalization. This gives them new properties and allows them to improve their performance for a given application. This review paper intends to understand how porous carbons involve the removal of pollutants from water, e.g., heavy metal ions, dyes, and organic or inorganic molecules. First, a general overview description of the different precursors and the manufacturing methods of porous carbons is illustrated. The second part is devoted to reporting some applications such using porous carbon materials as an adsorbent. It appears that the use of porous materials at different scales for these applications is very promising for wastewater treatment industries.

Green and plant-based adsorbent from tragacanth gum and carboxyl-functionalized carbon nanotube hydrogel bionanocomposite for the super removal of methylene blue dye

This study aims to prepare a hydrogel bionanocomposite (HBNC) as an efficient adsorbent and introduce it as a suitable replacement for petroleum-based adsorbents. Thus, tragacanth gum (TG), and carboxyl-functionalized carbon nanotube (CFCNT) were used as raw materials. HBNCs were prepared with the aid of ultrasonication, and different methods were employed to characterize them. The surface structures of the HBNCs were altered after the addition CFCNT into TG and exposure to ultrasound, as well. Transmission electron microscopy images showed CFCNTs were well dispersed in TG. Then, the adsorption of methylene blue (MB) was performed using these HBNCs. The removal efficiency was over 80% at optimized conditions. Nonlinear and linear forms of Langmuir, Freundlich, Dubinin-Radushkevich, Sips, and Redlich-Peterson (R-P) were applied to find the proper arrangement of MB onto the adsorbent. Using statistical equations, it was revealed that the process obeyed the linear R-P model, indicating a mixture of mono- and multilayer adsorption (but mostly monolayer). Also, pseudo-second-order was the appropriate kinetic model and suggested chemical adsorption. According to the thermodynamic calculations, this process was exothermic and spontaneous, and the type of interactions between HBNC and MB was physicochemical. Also, the diffusion study indicated that film diffusion is the primary mechanism.

Biomass-Based Activated Carbon and Activators: Preparation of Activated Carbon from Corncob by Chemical Activation with Biomass Pyrolysis Liquids

Pyrolysis liquids are the main products in biomass pyrolysis, and the strong acidity limits its utilization. Likewise, activators are required in the process of preparing biomass-based activated carbon, and current activators are usually chemical agents and not sustainable. Both issues are addressed with the new concept of using acidic pyrolysis liquids as the activator of biomass-based activated carbon. In the present research, corncob-based activated carbon was prepared with phosphoric acid and pyrolysis liquids (bio-oil and wood vinegar) as activators. The effects of activation temperature and the types of activators on the structure and surface chemical properties of activated carbon were investigated. Results show that the adsorption performance and specific surface area of activated carbon prepared with bio-oil are not as good as that prepared with phosphoric acid and wood vinegar, but its yield is relatively high. Some alkali and earth alkaline metals remain on the activated carbon prepared by bio-oil and wood vinegar. At 450 °C, the surface area and pore volume of activated carbon prepared with bio-oil and wood vinegar were much smaller than the ones prepared with phosphoric acid. Increasing the activation temperature may improve the performance of activated carbon. The specific surface area of activated carbon prepared with wood vinegar as the activator can reach 384.35 m²/g at an activation temperature of 850 °C, which is slightly inferior to that prepared with phosphoric acid as the activator. However, the adsorption amount of methylene blue exceeds the activated carbon prepared with phosphoric acid. This shows that wood vinegar can be used as an activator to prepare biomass-based activated carbon to achieve sustainability of the entire preparation process of biomass-based activated carbon.