Achieving high adsorption capacity and ultrafast removal of methylene blue and Pb2+ by graphene-like TiO2@C

Adsorption of copper from water using TiO2-modified activated carbon derived from orange peels and date seeds: Response surface methodology optimization

This study evaluated the application and efficiency of modified activated carbon in the removal of copper (Cu) from synthetic aquatic samples. The surface of activated carbon derived from orange peel (AC-OP) and date seeds (AC-DS) have been modified by Titanium dioxide nanoparticles (TiO2 NPs) (1:10 wt% mixing ratio) and used in a series of experiments designed by Response Surface Methodology (RSM) incorporating Central Composite Design (CCD). The Brunauer-Emmett-Teller (BET) test demonstrated that the modification has increased the surface area of AC-OP from 2.40 to 6.06 m2 g-1 and AC-DS from 51.10 to 81.37 m2 g-1. Effects of pH (1-7), ion initial concentration (10-60 mg L-1), adsorbent dose (0.5-8 g L-1), and contact time (0.4-6 h) have been investigated. The results showed that the optimum conditions for TiO2-modified AC-OP (OP-TiO2) are pH 5, initial concentration of 24.6 mg L-1, adsorbent dose of 4.9 g L-1, and contact time of 3.6 h. The optimum conditions for TiO2-modified AC-DS (DS-TiO2) are pH 6.4, initial concentration of 21.2 mg L-1, adsorbent dose of 5 g L-1, and contact time of 3.0 h. The modified quadratic models represented the results well with regression coefficients of 0.91 and 0.99 for OP-TiO2 and DS-TiO2, respectively. The maximum Cu removal for OP-TiO2 and DS-TiO2 were 99.90 % and 97.40 %, and the maximum adsorption capacity was found to be 13.34 and 13.96 mg g-1, respectively. Kinetic data have been fitted to pseudo first-order, pseudo second-order, intra-particle diffusion, and Elovich models. The pseudo second-order showed a better fit to the experimental data (R2 > 98 %). This study demonstrates the successful development of modified activated carbon derived from orange peels and date seeds, modified by TiO2 nanoparticles, for efficient adsorption of copper ions from water. The findings contribute to understanding the adsorption mechanism and provide valuable insights for designing environmentally friendly adsorbents.

Chitosan-induced self-assembly of montmorillonite nanosheets along the end-face for methylene blue removal from water

In this study, chitosan-induced self-assembly of montmorillonite nanosheets (MMTNS) along the end-face to form the layered and porous structured composite with high adsorption capacity towards MB dye wastewater was investigated. The self-assembly process was driven by the hydrogen-bond interaction among -OH groups distributed along the end-face of MMTNS and -NH₂ groups on chitosan (CS) chain, which finally formed the infinite two-dimensional lamellae. This technology remained the exposed adsorption sites on MMTNS surface, and solved the separation issue of spent MMTNS from water, making MMTNS/CS an excellent adsorption material for macromolecular MB dye. The maximum adsorption capacity of MMTNS/CS towards MB reached 243 mg/g, which was achieved via the Na⁺- exchange, hydrogen-bond and n-π stacking interactions with MB molecules. This work aimed at breaking through the bottleneck of small adsorption capacity of traditional MMT adsorbents, solving the problem of solid-liquid separation of nanosheets, and effectively reducing the adsorption cost, which might guide an important direction for adsorption material design and development in the future.

PLA-ZnO/TiO2 Nanocomposite Obtained by Ultrasound-Assisted Melt-Extrusion for Adsorption of Methylene Blue

Access to fresh water is an increasing concern worldwide. The contamination of this vital liquid is largely caused by discharges of pollutants into rivers and seas from different types of industries. Waste dyes from different industries have been classified as harmful to health. In this study, polymeric nanomaterials based on polylactic acid (PLA) and nanoparticles of titanium dioxide (TiO₂) and zinc oxide (ZnO) modified by ultrasound-assisted extrusion were obtained. These materials were evaluated by FTIR, DRX, TGA, DSC, SEM and methylene blue adsorption. From the results of the physicochemical characterizations, it was possible to observe the presence of TiO₂ and ZnO nanoparticles dispersed in the polymeric matrix, increasing the crystallinity and thermal stability of the polymer. In addition, a good dispersion of the nanoparticles could be seen by means of SEM, due to the extrusion assisted by ultrasound. The methylene blue dye adsorption tests revealed that the best result was 98% dye adsorption in a time of 13 min for the 1.5% PZT sample. Additionally, this material could be used for 3 adsorption cycles without affecting its adsorbent properties.

Facile Preparation of Porous Carbon Derived from Pomelo Peel for Efficient Adsorption of Methylene Blue

Pomelo peel waste-derived porous carbon (PPPC) was prepared by a facile one-step ZnCl₂ activation method. The preparation parameters of PPPC were the mass ratio of ZnCl₂ to pomelo peel of 2:1, carbonization temperature of 500 °C, and carbonization time of 1 h. This obtained PPPC possessed abundant macro-,meso-, and micro-porous structures, and a large specific surface area of 939.4 m² g^-1. Surprisingly, it had excellent adsorption ability for methylene blue, including a high adsorption capacity of 602.4 mg g^-1 and good reusability. The adsorption isotherm and kinetic fitted with Langmuir and pseudo-second order kinetic models. This work provides a novel strategy for pomelo peel waste utilization and a potential adsorbent for treating dye wastewater.

In situ engineering of highly conductive TiO2/carbon heterostructure fibers for enhanced electrocatalytic degradation of water pollutants

Rational design of nanocomposite electrode materials with high conductivity, activity, and mechanical strength is critical in electrocatalysis. Herein, freestanding, flexible heteronanocomposites were fabricated in situ by carbonizing electrospun fibers with TiO₂ nanoparticles on the surface for electrocatalytic degradation of water pollutants. The carbonization temperature was observed as a dominant parameter affecting the characteristics of the electrodes. As the carbonization temperature increased to 1000 °C, the conductivity of the electrode was significantly enhanced due to the high degree of graphitization (I_D/I_G ratio 1.10) and the dominant rutile phase. Additionally, the formation of TiO₂ protrusions and the C-Ti heterostructure were observed at 1000 °C, which contributed to increasing the electrocatalytic activity. When 1.5 V (vs. Ag/AgCl) was employed, electrocatalytic experiments using the electrode achieved 90% degradation of crystal violet and 10.9-87.5% for an array of micropollutants. The electrical energy-per-order (EEO) for the removal of crystal violet was 0.7 kWh/m³/order, indicative of low-energy requirement. The efficient electrocatalytic activity can be ascribed to the fast electron transfer and the strong ability to generate hydroxyl radicals. Our findings expand efforts for the design of highly conductive heteronanocomposites in a facile in situ approach, providing a promising perspective for the energy-efficient electrocatalytic degradation of water pollutants.

Removal of Methylene Blue from Aqueous Solution Using Black Tea Wastes: Used as Efficient Adsorbent

The biosorbent black tea wastes (BTW) after preliminary treatments was used in this study for the removal of methylene blue (M.B) from aqueous solution. The removal of M.B from aqueous solution was studied as a function of time, initial concentration of M.B temperature, pH, and BTW dosage. The optimum time for equilibration was achieved in 3 min. The optimum dosage of adsorbent was found to be 0.4 g. Various kinetic models were applied to the sorption kinetic data in which the obtained data was best explained by the pseudo-second-order model ( $R^2=0.99$ ) with a rate constant K2 of 0.0714–0.0763 g.mg-1 min-1. Additionally, the calculated amount of adsorption was approximately equal to the experimentally determined value. The isotherm data was best fitted to the Langmuir model rather than the Freundlich model. The intraparticle diffusion model exhibited the process to be diffusion dependent. The various organic functional groups on the surface of BTW played a significant role in the sorption of the selected dye. Consequently, BTW has the prospective to act as a potential sorbent for the removal of other contaminants from aquatic media as well.

Granular activated carbon-supported titanium dioxide nanoparticles as an amendment for amending copper-contaminated sediments: Effect on the pH in sediments and enzymatic activities

The problem of heavy metal pollution in sediments attracts increasing attention with the process of industrialization. In this study, a novel sediments amendment granular activated carbon (GAC)-supported titanium dioxide nanoparticles (GATN) was synthesized to amend copper (Cu)-contaminated sediments. The effect of the amendments on the potential mobility and bioavailability of Cu was evaluated by the concentration of Cu in the overlying water and the chemical speciations of Cu in sediments. After 35 days of incubation, GATN and GAC were separated from the GATN-amended sediments and the GAC-amended sediments. The European Community Bureau of Reference (BCR) sequence extraction procedure was performed on the separated sediments. Compared with the control group, the addition of 20% GATN amended sediments for 35 days, the Cu concentration in the overlying water decreased by 90.75%. Compared with original sediments, the exchangeable fraction and reducible fraction of Cu decreased from 42.30% to 17.36%-3.63% and 6.57%, respectively, and the oxidizable fraction and residual fraction of Cu increased from 13.57% to 26.77%-33.21% and 56.58%, respectively. The potential mobility and bioavailability of Cu were significantly reduced. According to the BCR sequence extraction results of the remaining sediments after the separation of the GATN, the Cu adsorbed on the GATN surface is mainly an oxidizable fraction, which is generated by the complexation reaction of hydroxyl (-OH) and Cu²⁺. Meanwhile, the present of GATN also can enhance the remediation capacity of sediments, which plays an important role during the amendment process. The pH was measured after GATN-amended sediments adding. Results showed that GATN improved their remediation capacity of sediments by optimizing the pH in sediments. The enzyme activity-experiment indicated that GATN effectively reduces the biological toxicity of Cu in Cu-contaminated sediments. Results verified that GATN, as a sediments amendment, has good application potential.

Remediation of copper contaminated sediments by granular activated carbon-supported titanium dioxide nanoparticles: Mechanism study and effect on enzyme activities

After much effort, the remediation of heavy metal contaminated sediments still remains physically hard and technically challenging issue to resolve. In this study, granular activated carbon-supported titanium dioxide nanoparticles (GAC-TiO₂ NPs) are synthesized to remedy heavy metal copper (Cu) contaminated sediments. The concentration and chemical speciation of Cu in overlying water, interstitial water and contaminated sediments are fully assessed to examine the remediation effect of GAC-TiO₂ NPs. The GAC-TiO₂ NPs are separated from GAC-TiO₂ NPs-remedied sediments and characterized by X-ray photoelectron spectra (XPS), which reveals the mechanism of GAC-TiO₂ NPs remedy Cu Contaminated sediments. The results show that after 35 days adding 20% GAC-TiO₂ NPs to contaminated sediments, the Cu concentration in the overlying water and interstitial water decreases 89.47% and 83.52%, respectively, and the exchangeable fraction (F-1) of Cu in sediments decreases from 43.91% to 7.49%. The percentage of residual fraction (F-4) increases sharply from 42.79% to 80.30%. XPS results show that hydroxyl (-OH) plays an important role in the remediation process. The synergistic effects of pH, phosphorus concentration and organic matter (OM) content on the remediation effect are explored. When the pH value is 8, phosphorus concentration is 0.32 mg/L and OM content is 151.2 g/kg, adding 20% GAC-TiO₂ NPs achieves the best remediation effect on Cu contaminated sediment. Biological enzyme-activity experiments prove that GAC-TiO₂ NPs not only reduce the bioavailability and biotoxicity of Cu, but also effectively suppress the negative effects of granular activated carbon (GAC) on enzyme activities. All these results indicate that GAC-TiO₂ NPs is an environmentally friendly remediation material for Cu contaminated sediments with high-potential applications.

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

A novel composite of SiO2 decorated with nano ferrous oxalate (SDNF) for efficient and highly selective removal of Pb2+ from aqueous solutions

Developing a material with high adsorption capacity and selectivity to remove lead from Pb²⁺ polluted wastewater is of vital importance for environment protection and resources utilization. In this study, a novel composite, SiO₂ decorated with nano ferrous oxalate (SDNF), was prepared from natural biotite containing ores to remove Pb²⁺. Pseudo-first-order kinetic (R² = 0.99) and Langmuir models (R² = 0.99) fitted the data well, manifesting that Pb²⁺ adsorption process was monolayer adsorption. The maximum Pb²⁺ adsorption capacity was identified as 446.98 mg/g. SEM and TEM images showed that nano ferrous oxalate with average size of 11.51 nm was coated on the surface of ores, and their distributions were uniform. Results of XRD, XPS, FTIR and zeta potential indicated that ion exchange, surface complexation and electrostatic attraction interaction were involved in the remvoal of Pb²⁺, and the ion exchange between Fe²⁺ and Pb²⁺ played a major role. Moreover, both Cd²⁺ and Zn²⁺ removal efficiency are less than 2 % in Pb-Cd or Pb-Zn coexisted solution, indicating the composite possessed high selectivity for Pb²⁺ removal. All above results indicated that the composite was a material with high adsorption capacity and selectivity for Pb²⁺, which was suitable for remediation of Pb²⁺ pollution from Pb²⁺ containing wastewater.

Recent progress and advances in the environmental applications of MXene related materials

MXenes are a new type of two-dimensional (2D) transition metal carbide or carbonitride material with a 2D structure similar to graphene. The general formula of MXenes is M_n+1X_nT_x, in which M is an early transition metal element, X represents carbon, nitrogen and boron, and T is a surface oxygen-containing or fluorine-containing group. These novel 2D materials possess a unique 2D layered structure, large specific surface area, good conductivity, stability, and mechanical properties. Benefitting from these properties, MXenes have received increasing attention and emerged as new substrate materials for exploration of various applications including, energy storage and conversion, photothermal treatment, drug delivery, environmental adsorption and catalytic degradation. The progress on various applications of MXene-based materials has been reviewed; while only a few of them covered environmental remediation, surface modification of MXenes has never been highlighted. In this review, we highlight recent advances and achievements in surface modification and environmental applications (such as environmental adsorption and catalytic degradation) of MXene-based materials. The current studies on the biocompatibility and toxicity of MXenes and related materials are summarized in the following sections. The challenges and future directions of the environmental applications of MXene-based materials are also discussed and highlighted.

Ultra-Highly Efficient Removal of Methylene Blue Based on Graphene Oxide/TiO2/Bentonite Sponge

An ultra-highly efficient Graphene Oxide/TiO₂/Bentonite (GO/TiO₂/Bent) sponge was synthesized using an in situ hydrothermal method. GO/TiO₂/Bent sponge with a GO mass concentration of 10% exhibited the highest treatment efficiency of methylene blue (MB), combining adsorption and photocatalytic degradation, and achieved a maximum removal efficiency of 100% within about 70 min. To further prove the ultra-high removal capacity of the sponge, the concentration of MB in water increased to ten times the original concentration. At so high a MB concentration, the removal rate was still as high as 80% in 90 min. The photocatalytic mechanism of GO/TiO₂/Bent sponge was discussed through XPS, PL and radicals quenching experiments. Here Bent can immobilize TiO₂ and react with a photo-generated hole to increase the amount of hydroxyl radical; effectively enhancing the degradation of MB.GO sponge enlarges the sensitivity range of TiO₂ to visible light by increasing the charge separation of TiO₂ and reducing the recombination of photo-generated electron–hole pairs. Additionally, GO sponge with an interconnected porous structure provides an effective platform to immobilize TiO₂/bent and makes them be easily recovered. The as-prepared sponge develops a simple and cost-effective strategy to realize the ultra-highly efficient treatment of dyes in wastewater.

High-performance two-dimensional montmorillonite supported-poly(acrylamide-co-acrylic acid) hydrogel for dye removal

High-performance two-dimensional montmorillonite supported-poly (acrylamide-co-acrylic acid) hydrogel for dye removal was investigated. Montmorillonite cooperated with acrylamide and acrylic acid via polymerization, hydrogen-bond, amidation and electrostatic interactions to form the three-dimensional reticular-structured hydrogel with the free entrance for macromolecules. Adsorption tests revealed that the efficient removal (97%) for methylene blue at high concentration (200 mg/L) could be achieved via a small dose of hydrogel (0.5 g/L) within a short time (20 min). The excellent adsorption performance was profited from the electronegative surface and fully exposed reaction sites of two-dimensional montmorillonite, which could save the treatment cost and promote the removal effect compared with the conventional adsorbents. The adsorption process of methylene blue onto hydrogel could be fitted by both the pseudo-first-order and pseudo-second-order kinetics models, and the adsorption isotherm corresponded to the Sips model. The mechanism analysis based on Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements illustrated that the reaction between carboxyl groups and methylene blue molecules as well as the cation-exchange enabled the hydrogel performing extraordinary adsorption efficiency.

Adsorption of methylene blue onto porous carbon materials prepared from Na2EDTA

A simple self-activation preparation procedure and excellent adsorption performance for methylene blue.

A facile fabrication of sepiolite mineral nanofibers with excellent adsorption performance for Cd2+ ions

In this work, sepiolite mineral nanofibers are facilely prepared by a microwave-hydrogen peroxide method, and the bulk densities of the samples are adopted to evaluate the defibering effect.