Lead ferrite-activated carbon magnetic composite for efficient removal of phenol from aqueous solutions: synthesis, characterization, and adsorption studies

Excess secondary sludge reuse by H2O2 thermal dehydration

The excess of activated sludge generated in municipal wastewater treatment plants constitutes one of the challenging problems facing modern society. The high-water content of this waste makes difficult the transport, disposal, and management of these solids. In this work, activated sludge excess from a secondary clarifier has been dehydrated by means of a combination of temperature and hydrogen peroxide treatment. Three main operating variables have been considered to affect sludge dewaterability and filterability. Temperature (120-180 °C), hydrogen peroxide dose (0.01-0.03 M), and treatment time (20-60 min) influence have been assessed by completing a 15-run Box Behnken experimental design. Different output variables (water content, resistance to filtration, sedimentation volumetric index, extracellular polymeric substances, etc.) have been monitored. Generally, temperature seems to be the most influencing parameter to obtain a dehydrated sludge with acceptable management/disposal characteristics (sludge volume reduction and filterability). In line with the concept of circular economy, an attempt has been conducted to obtain a sustainable biosorbent from the dehydrated sludge generated in the previous stage. Optimum conditions of carbonization and activation revealed that the solid obtained at 400 °C by using ammonium nitrate as activation agent was the most efficient absorbent to eliminate some model compounds from water (namely, phenol, ofloxacin, and diuron); however, a clear improvement margin in the synthesis is foreseen.

Emerging iron-based mesoporous materials for adsorptive removal of pollutants: Mechanism, optimization, challenges, and future perspective

Iron-based materials (IBMs) have shown promise as adsorbents due to their unique physicochemical properties. This review provides an overview of the different types of IBMs, their synthesis methods, and their properties. Results found in the adsorption of emerging contaminants to a wide range of IBMs are discussed. The IBMs used were evaluated in terms of their maximum uptake capacity, with special consideration given to environmental conditions such as contact time, solution pH, initial pollutant concentration, etc. The adsorption mechanisms of pollutants are discussed taking into account the results of kinetic, isotherm, thermodynamic studies, surface complexation modelling (SCM), and available spectroscopic data. A current overview of molecular modeling and simulation studies related to density functional theory (DFT), surface response methodology (RSM), and artificial neural network (ANN) is presented. In addition, the reusability and suitability of IBMs in real wastewater treatment is shown. The review concludes with the strengths and weaknesses of current research and suggests ideas for future research that will improve our ability to remove contaminants from real wastewater streams.

Enhancing the efficiency of Ni(II), Cd(II), and Cu(II) adsorption from aqueous solution using schist/alginate composite: batch and continuous studies

The main aim of this research is focused on the synthesis of schist/alginate composite (SC/AL) adsorbent and its utilization for the removal of Ni(II), Cu(II), and Cd(II) from waste streams using batch and column processes. The characterization of developed adsorbent was performed by X-ray fluorescence, X-ray diffraction, FTIR, and BET analyses. The most influential operating parameters (pH, contact time, temperature and initial adsorbate concentration) on the adsorption capacity of pollutants were examined to evaluate the performance of developed adsorbent. The kinetic and equilibrium adsorption results at pH 5.0 indicated that SC/AL composite had good adsorption capacity (qmax) for Ni(II), Cu(II), and Cd(II) estimated at 124.79 mg/g, 111.78 mg/g, and 119.78 mg/g, respectively. From the kinetic viewpoint, the good fit of pseudo-first-order kinetic model to the kinetic adsorption data indicated that dominant interaction of heavy metals with SC/AL composite was physisorption. The results of thermodynamic studies indicated that the adsorption of heavy metals onto SC/AL composite was endothermic and spontaneous in nature. The adsorption capacity of developed adsorbent could still reach relatively 85% of the original one after completing fifth cycle. Therefore, the reusability results of SC/AL composite were quite satisfied, making the developed adsorbent a commercially attractive and green method. Finally, in column studies, the effect of initial concentration of pollutants at pH 5.0 on the removal of heavy metal ions was investigated. The Thomas and Yoon-Nelson models provided a satisfactory explanation for the results of column data.

Facile Synthesis of the Polyaniline@Waste Cellulosic Nanocomposite for the Efficient Decontamination of Copper(II) and Phenol from Wastewater

The existence of heavy metals and organic pollutants in wastewater is a threat to the ecosystem and a challenge for researchers to remove using common technology. Herein, a facile one-step in situ oxidative polymerization synthesis method has been used to fabricate polyaniline@waste cellulosic nanocomposite adsornt, polyaniline-embedded waste tissue paper (PANI@WTP) to remove copper(II) and phenol from the aqueous solution. The structural and surface properties of the synthesized materials were examined by XRD, FTIR, TEM, and a zeta potential analyzer. The scavenging of the Cu(II) and phenol onto the prepared materials was investigated as a function of interaction time, pollutant concentration, and solution pH. Advanced kinetics and isotherms modeling is used to explore the Cu(II) ion and phenol adsorption mechanisms. The synthesized PANI@WTP adsorbent showed a high intake capacity for Cu(II) than phenol, with the maximum calculated adsorption capacity of 605.20 and 501.23 mg g^-1, respectively. The Langmuir equilibrium isotherm model is well-fitted for Cu(II) and phenol adsorption onto the PANI@WTP. The superior scavenging capability of the PANI@WTP for Cu(II) and phenol could be explained based on the host-guest interaction forces and large active sites. Moreover, the efficiency of the PANI@WTP for Cu(II) and phenol scavenging was excellent even after the five cycles of regeneration.

Application of Pb-Fe spinel-activated carbon for phenol removal from aqueous solutions: fixed-bed adsorption studies

Fixed-bed studies for phenol uptake from water were carried out using a novel Pb-Fe spinel-activated carbon adsorbent. A characterization phase including TGA, FTIR, SEM, and BET analyses was performed for the developed active carbon. In column studies, the influence of initial phenol concentration, column bed height, and the solution flow rate was investigated at natural pH. Adsorption of phenol onto Pb-Fe spinel-activated carbon composite and pristine activated carbon was analyzed in the form of breakthrough curves. Under optimum conditions, the maximum adsorption capacities for the magnetic active carbon composite and pristine activated carbon were found to be 113.95 and 102.61 mg/g, respectively. Results indicated that the adsorption capacity of adsorbent for all examined conditions was higher than that obtained for unmodified activated carbon because the composite contains additional metal hydroxides compared with the pristine activated carbon. The Yoon and Nelson, Thomas, and instantaneous local equilibrium (ILE) models were used to explain column data collected under different operating conditions. Finally, the results of the continuous adsorption process were explained successfully using the Yoon-Nelson and Thomas models. Thus, the phenol adsorption on Pb-Fe@MAC was a feasible operation to be performed in fixed-bed mode.

Rapid growth of MXene-based membranes for sustainable environmental pollution remediation

Water consumption has grown in recent years due to rising urbanization and industry. As a result, global water stocks are steadily depleting. As a result, it is critical to seek strategies for removing harmful elements from wastewater once it has been cleaned. In recent years, many studies have been conducted to develop new materials and innovative pathways for water purification and environmental remediation. Due to low energy consumption, low operating cost, and integrated facilities, membrane separation has gained significant attention as a potential technique for water treatment. In these directions, MXene which is the advanced 2D material has been explored and many applications were reported. However, research on MXene-based membranes is still in its early stages and reported applications are scatter. This review provides a broad overview of MXenes and their perspectives, including their synthesis, surface chemistry, interlayer tuning, membrane construction, and uses for water purification. Application of MXene based membrane for extracting pollutants such as heavy metals, organic contaminants, and radionuclides from the aqueous water bodies were briefly discussed. Furthermore, the performance of MXene-based separation membranes is compared to that of other nano-based membranes, and outcomes are very promising. In order to shed more light on the advancement of MXene-based membranes and their operational separation applications, significant advances in the fabrication of MXene-based membranes is also encapsulated. Finally, future prospects of MXene-based materials for diverse applications were discussed.

Arsenic Oxidation and Removal from Water via Core-Shell MnO2@La(OH)3 Nanocomposite Adsorption

Arsenic (As(III)), more toxic and with less affinity than arsenate (As(V)), is hard to remove from the aqueous phase due to the lack of efficient adsorbents. In this study, a core-shell structured MnO₂@La(OH)₃ nanocomposite was synthesized via a facile two-step precipitation method. Its removal performance and mechanisms for As(V) and As(III) were investigated through batch adsorption experiments and a series of analysis methods including the transformation kinetics of arsenic species in As(III) removal, FTIR, XRD and XPS. Solution pH could significantly influence the removal efficiencies of arsenic. The adsorption process of As(V) occurred rapidly in the first 5 h and then gradually decreased, whereas the As(III) removal rate was relatively slower. The maximum adsorption capacities of As(V) and As(III) were up to 138.9 and 139.9 mg/g at pH 4.0, respectively. For As(V) removal, the inner-sphere complexes of lanthanum arsenate were formed through the ligand exchange reactions and coprecipitation. The oxidation of As(III) to the less toxic As(V) by δ-MnO₂ and subsequently the synergistic adsorption process by the lanthanum hydroxide on the MnO₂@La(OH)₃ nanocomposite to form lanthanum arsenate were the dominant mechanisms of As(III) removal. XPS analysis indicated that approximately 20.6% of Mn in the nanocomposite after As(III) removal were Mn(II). Furthermore, a small amount of Mn(II) and La(III) were released into solution during the process of As(III) removal. These results confirm its efficient performance in the arsenic-containing water treatment, such as As(III)-contaminated groundwater used for irrigation and As(V)-contaminated industrial wastewater.