Enhanced removal of p-nitrophenol from aqueous media by montmorillonite clay modified with a cationic surfactant

Efficient removal of p-nitrophenol from water by imidazolium ionic liquids functionalized cellulose microsphere

Removing p-nitrophenol (PNP) from water resources is crucial due to its significant threat to the environment and human health. Herein, imidazolium ionic liquids with short/long alkyl chain ([C2VIm]Br and [C8VIm]Br) modified cellulose microspheres (MCC-[C2VIm]Br and MCC-[C8VIm]Br) were synthesized by radiation method. To examine the impact of adsorbent hydrophilicity on adsorption performance, batch and column experiments were conducted for PNP adsorption. The MCC-[C2VIm]Br and MCC-[C8VIm]Br, with an equivalent molar import amount of ionic liquids, exhibited maximum adsorption capacities of 190.84 mg/g and 191.20 mg/g for PNP, respectively, and the adsorption equilibrium was reached within 30 min. Both adsorbents displayed exceptional reusability. Integrating the findings from XPS and FTIR analyses, and AgNO3 identification, the suggested adsorption mechanism posited that the adsorbents engaged with PNP through ion exchange, hydrogen bonds and π-π stacking. Remarkably, the hydrophobic MCC-[C8VIm]Br exhibited superior selectivity for PNP than the hydrophilic MCC-[C2VIm]Br, while had little effect on adsorption capacity and rate. MCC-[C8VIm]Br-2 with high grafting yield increased the adsorption capacity to 327.87 mg/g. Moreover, MCC-[C8VIm]Br-2 demonstrated efficient PNP removal from various real water samples, and column experiments illustrated its selective capture of PNP from groundwater. The promising adsorption performance indicates that MCC-[C8VIm]Br-2 holds potential for PNP removal from wastewater.

New Methodology for Modifying Sodium Montmorillonite Using DMSO and Ethyl Alcohol

Modified clays with organic molecules have many applications, such as the adsorption of pollutants, catalysts, and drug delivery systems. Different methodologies for intercalating these structures with organic moieties can be found in the literature with many purposes. In this paper, a new methodology of modifying Sodium Montmorillonite clays (Na-Mt) with a faster drying time was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET, and thermogravimetric analysis (TG and DTG). In the modification process, a mixture of ethyl alcohol, DMSO, and Na-Mt were kept under magnetic stirring for one hour. Statistical analysis was applied to evaluate the effects of the amount of DMSO, temperature, and sonication time on the modified clay (DMSO-SMAT) using a 23-factorial design. XRD and FTIR analyses showed the DMSO intercalation into sodium montmorillonite Argel-T (SMAT). An average increase of 0.57 nm for the interplanar distance was found after swelling with DMSO intercalation. BET analysis revealed a decrease in the surface area (from 41.8933 m2/g to 2.1572 m2/g) of Na-Mt when modified with DMSO. The porosity increased from 1.74 (SMAT) to 1.87 nm (DMSO-SMAT) after the application of the methodology. Thermal analysis showed a thermal stability for the DMSO-SMAT material, and this was used to calculate the DMSO-SMAT formula of Na[Al5Mg]Si12O30(OH)6 · 0.54 DMSO. Statistical analysis showed that only the effect of the amount of DMSO was significant for increasing the interlayer space of DMSO-SMAT. In addition, at room temperature, the drying time of the sample using this methodology was 30 min.

Cetyltrimethylammonium Bromide-Modified Laponite@Diatomite Composites for Enhanced Adsorption Performance of Organic Pollutants

This work aims to enhance the adsorption performance of Laponite @diatomite for organic pollutants by modifying it with cetyltrimethylammonium bromide (CTAB). The microstructure and morphology of the CTAB-modified Laponite @diatomite material were characterized using SEM, XRD, FTIR, BET, and TG. Furthermore, the influences of key parameters, containing pH, adsorbent dosage, reaction time, and reaction temperature, on the adsorption process were investigated. The kinetics, thermodynamics, and isotherm models of the adsorption process were analyzed. Finally, potential adsorption mechanisms were given based on the characterization. The research findings indicate that CTAB-La@D exhibits good adsorption performance toward Congo red (CR) over a broad pH range. The maximum adsorption capacity of CR was 451.1 mg/g under the optimum conditions (dosage = 10 mg, contact time = 240 min, initial CR concentration = 100 mg/L, temperature = 25 °C, and pH = 7). The adsorption process conformed to the pseudo-second-order kinetic model, and the adsorption isotherms indicated that the adsorption process of CR was more in line with the Langmuir model, and it was physical adsorption. Thermodynamic analysis illustrates that the adsorption process is exothermic and spontaneous. Additionally, the mechanisms of electrostatic adsorption and hydrophobic effect adsorption of CR were investigated through XPS and FTIR analysis. This work provides an effective pathway for designing high-performance adsorbents for the removal of organic dye, and the synthesized materials hold great capability for practical utilization in the treatment of wastewater.

Resource utilization of wastepaper and bentonite: Cu(II) removal in the aqueous environment

Contamination of heavy metals has always been a pressing concern. The dry-wet alternately treated carboxymethylcellulose bentonite (DW-CB) was successfully prepared by intercalating bentonite (BT) with carboxymethyl cellulose (CMC) obtained by solvent processes using enzymatically digested wastepaper as cellulosic raw material, and the adsorption capacity of Cu2+ on DW-CB in aqueous solution was investigated. A 98.18 ± 2.31 % removal efficiency was achieved by 4 g/L of DW-CB after 8 h in a solution containing 100 mg/L of Cu2+, which were 4.1 times and 1.5 times of that of BT and adsorbent prepared without alternating dry-wet process, respectively. The introduction of -COOH groups during the preparation of DW-CB enhanced the electrostatic interaction between DW-CB and Cu2+, which was the main driving force for Cu2+ removal. The pseudo-first-order kinetic model and Langmuir model better described the adsorption process and adsorption capacity of Cu2+ on DW-CB. DW-CB still showed high removal of Cu2+ (19.61 ± 0.99 mg/g) in the presence of multiple metal ions, while exhibiting the potential for removal of Zn2+, Mg2+ and K+, especially Mg2+ (22.69 ± 1.48 mg/g). However, the interactions of organics with Cu2+ severely affected the removal of Cu2+ by DW-CB (removal efficiency: 17.90 ± 4.17 % - 95.33 ± 0.27 %). In this study, an adsorbent with high targeted adsorption of Cu2+ was prepared by utilizing wastepaper and BT, which broadened the way of wastepaper resource utilization and had good economic and social benefits.

Electrocatalytic degradation of p-nitrophenol on metal-free cathode: Superoxide radical (O2•-) production via molecular oxygen activation

Although metal-free electrodes in molecular oxygen-activated Fenton-like wastewater treatment technologies have been developed, the reactive oxygen species (ROS) generation mechanisms are still not sufficiently clear. As a typical example of refractory phenolic wastewater, p-nitrophenol (PNP) has been widely studied. This study demonstrated the critical role of superoxide radicals (O2•-) in PNP degradation by metal-free electrodes through electron spin resonance (ESR), ROS quenching, and density functional theory (DFT) tests. The most superior metal-free electrode exhibited a mass activity of approximately 133.5 h-1 gcatalyst-1. Experimental and theoretical studies revealed the mechanism of O2•- generation via oxygen activation, including one- and three-electron transfer pathways, and found that O2•- mainly attacked the nitro group of PNP to degrade and transform the pollutant. This study enhances the mechanistic understanding of metal-free materials in the electrochemical degradation of refractory pollutants.

Removal of p-Nitrophenol by Adsorption with 2-Phenylimidazole-Modified ZIF-8

Petrochemical wastewater contains p-nitrophenol, a highly toxic, bioaccumulative and persistent pollutant that can harm ecosystems and environmental sustainability. In this study, ZIF-8-PhIm was prepared for p-nitrophenol removal from petrochemical wastewater using solvent-assisted ligand exchange (SALE) with 2-phenylimidazole(2-PhIm). The ZIF-8-PhIm's composition and structure were characterised using the XRD, SEM, FT-IR, ¹H NMR, XPS and BET methods. The adsorption effect of ZIF-8-PhIm on p-nitrophenol was investigated with the static adsorption method. Compared to the ZIF-8 materials, ZIF-8-PhIm exhibited stronger π-π interactions, produced a multistage pore structure with larger pore capacity and size, and had increased hydrophilicity and exposure of adsorption sites. Under optimised conditions (dose = 0.4 g/L, T = 298 K, C₀ = 400 mg/L), ZIF-8-PhIm achieved an adsorption amount of 828.29 mg/g, which had a greater p-nitrophenol adsorption capacity compared to the ZIF-8 material. The Langmuir isotherm and pseudo-second-order kinetic models appropriately described the p-nitrophenol adsorption of ZIF-8-PhIm. Hydrogen bonding and π-π interactions dominated the p-nitrophenol adsorption of ZIF-8-PhIm. It also had relatively good regeneration properties.

Interlayer structure and dynamic properties of CTMAB-montmorillonite: experiment and molecular dynamics

The intercalation of cetyltrimethylammonium bromide (CTMAB) into montmorillonite will cause interlayer expansion and surface charge reversal. In this study, CTMAB-Mt is prepared by adding CTMAB with different multiples of montmorillonite cation exchange capacity (CEC), and the intercalated CTMAB structural arrangement, as well as the dynamics behavior, are investigated by combining molecular dynamics (MD) simulation with experimental characterization. According to RDF analysis of MD simulations, the interaction between CTMA⁺ and the surface of montmorillonite is mostly electrostatic interaction and hydrogen bond production. At low loading (≤1.00CEC), the XRD profile exhibits a peak value corresponding to one type of intercalation structure and interlayer spacing, but at high loading (>1.00CEC), two peaks are visible, each of which has a fixed value but a varied strength, corresponding to the existence of two types of expanded structures. The d-spacing (d ₀₀₁) values obtained from MD simulations are quite close to XRD values when CTMAB loading is lower than 1.00CEC. Density distribution profiles obtained from MD analysis reveal that as loading increases, CTMA⁺ is arranged in the interlayer from a monolayer to a bilayer and then to a pseudo-trilayer. At high loadings (>1.00CEC), due to the fact that the excess loading leads to inhomogenous intercalation, XRD demonstrates the existence of two different arrangements: bilayer and pseudo-trilayer. The self-diffusion coefficients of MD simulations show that the dynamic behavior of CTMA⁺ is influenced by both the interlayer space and the electrostatic interaction of the montmorillonite clay. The abrupt rise in interlayer spacing increases mobility, whereas the increased interaction between alkyl chains decreases mobility.

Organic-Inorganic Hybrid Pigments Based on Bentonite: Strategies to Stabilize the Quinoidal Base Form of Anthocyanin

Anthocyanins are one of the natural pigments that humanity has employed the most and can substitute synthetic food dyes, which are considered toxic. They are responsible for most purple, blue, and red pigment nuances in tubers, fruits, and flowers. However, they have some limitations in light, pH, oxygen, and temperature conditions. Combining biomolecules and inorganic materials such as clay minerals can help to reverse these limitations. The present work aims to produce materials obtained using cetyltrimethylammonium bromide in bentonite clay for incorporation and photostabilization of anthocyanin dye. Characterizations showed that the organic molecules were intercalated between the clay mineral layers, and the dye was successfully incorporated at a different pH. Visible light-driven photostability tests were performed with 200 h of irradiation, confirming that the organic-inorganic matrices were efficient enough to stabilize the quinoidal base form of anthocyanin. The pigment prepared at pH 10 was three-fold more stable than pH 4, showing that the increase in the synthesis pH promotes more stable colors, probably due to the stronger intermolecular interaction obtained under these conditions. Therefore, organobentonite hybrids allow to stabilize the fragile color coming from the quinoidal base form of anthocyanin dyes.

Effect of pH, ionic strength, and temperature on the adsorption behavior of Acid Blue 113 onto mesoporous carbon

Mesoporous carbon (MC) derived from cassava starch was used to remove Acid Blue 113 azo dye from aqueous solutions. The influence of temperature, pH, ionic strength, and the adsorbent dose was investigated in a set of batch experiments. Experimental data showed that Acid Blue 113 adsorption was higher in the acid pH range than in the alkaline one, that dye adsorption increases when the ionic strength and temperature increase, and that adsorption results presented a good correlation with the Langmuir isotherm model. The adsorption capacity of MC was 295 mg g^-1, at pH = 7.0 and 298 K, respectively. Zeta potential (ζ) showed the compression of the diffuse double layer of adsorbent with an increase in temperature and ionic strength, promoting the decrease of electrostatic repulsion between the negatively charged surface of the carbon particles and the anionic dye. Thermodynamic results demonstrate that the adsorption process was spontaneous and endothermic. Moreover, for the first time, this work has demonstrated that the pH, temperature, and ionic strength of the aqueous medium are also able to change the surface charge of carbon-based adsorbents and surely influence the adsorption capacity. Finally, the regeneration of the adsorbent by the photo-Fenton reaction regenerated the adsorption capacity of the adsorbent without generating secondary pollution to the environment.

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Removal of p-Nitrophenol from simulated sewage using steel slag: Capability and mechanism

The steel slag was investigated for the removal of p-nitrophenol (4-NP) from simulated sewage by batch adsorption and fixed-bed column absorption experiments. The results showed that the maximum adsorption capacity was 109.66 mg/g at 298 K, pH of 7, initial concentration 100 mg/L, and dose 0.8 g/L. The adsorption process fitted the Langmuir isothermal adsorption model and followed pseudo-second-order kinetic models, the activation energy of adsorption (Ea) was 10.78 kJ/mol, which indicated that the adsorption was single-molecule layer physical adsorption. The regeneration efficiency was still maintained at 84.20% after five adsorption-desorption cycles. The column adsorption experiments showed that the adsorption capacity of the Thomas model reached 13.69 mg/g and the semi-penetrating time of the Yoon-Nelson model was 205 min at 298 K. Fe₃O₄ was identified as the main adsorption site by adsorption energy calculation, XRD and XPS analysis. The FT-IR, Zeta potential, and ionic strength analysis indicated that the adsorption mechanism was hydrogen bonding interaction and electrostatic interaction. This work proved that steel slag could be utilized as a potential adsorbent for phenol-containing wastewater treatment.

Experimental and modeling investigation of organic modified montmorillonite with octyl quaternary ammonium salt

The sodium montmorillonite was organic modified with three kinds of quaternary ammonium salts containing 1 to 3 octyl chains, and then the organic montmorillonite was studied by FT-IR, XRD, and TG characterization as well as Monte Carlo simulations, to explore the influence of the number of octyl chains and the loading of intercalated cations on the basal spacing (d₀₀₁) of the modified montmorillonite complexes. According to the distribution of intercalated quaternary ammonium cations and the energy change of the montmorillonite complexes, a reasonable explanation was given for the enlargement of the interlayer space. The results of experimental characterization and Monte Carlo simulations show that all the three intercalation agents can enlarge the interlayer space of montmorillonite complexes. The more the number of octyl chains in the salt, the more significant expanding effect on the interlayer space. The three intercalation cations exhibited a distribution arranged from mono-layered to multi-layered structure as the loading of intercalated cations increases.

Synthesis and characterization of solid-state Fe-exchanged nano-bentonite and evaluation of methyl orange adsorption

A new adsorbent was synthesized using ion-exchange between iron salts and bentonite modified with acetyl trimethylammonium bromide (CTAB) in the solid phase. Ion-exchange was performed in the solid state at a temperature of 100 °C for 2 min. Various analyses such as X-ray diffraction (XRD), scanning electron microscopy (SEM), porosity measurement (BET), infrared Fourier transform (FT-IR), transmission electron microscopy (TEM), X-ray energy diffraction (EDX), and thermal weighing (TGA) were used to characterize the synthesized nano-adsorbents. Under optimal conditions (pH = 7, time 60 min, concentration of dye solution 150 ppm, and amount of nano-adsorbent 0.75 g/l), the modified nano-adsorbent absorbed 73% of the methyl orange (MO) dye. Adsorption isotherm studies and kinetic model showed that the pseudo-second-order model and Langmuir equation agree with the obtained results. After three reductions of the modified nano-adsorbent in the photo-Fenton process, the dye absorption percentage was 69.50%.

Cleanup of oiled shorelines using a dual responsive nanoclay/sodium alginate surface washing agent

Oil spills may affect ecosystems and endanger public health. In this study, we developed a novel and dual responsive nanoclay/sodium alginate (NS) washing fluid, and systematically evaluated its application potential in oiled shoreline cleanup. The characterization results demonstrated that sodium alginate combined with nanoclay via hydrogen bonds, and was inserted into the interlayer spacing of nanoclay. Adding sodium alginate reduced surface and interfacial tensions, while increasing the viscoelasticity of the washing fluid. Batch experiments were conducted to investigate oil removal performance under various conditions. Additionally, the factorial design analysis showed that three single factors (temperature, oil concentration, and salinity), and two interactive effects (temperature/salinity; and oil concentration/HA) displayed significant effects on the oil removal efficiency of the NS washing fluid. Compared to the commercial surfactants, the NS composite exhibited satisfactory removal efficiencies for treating oily sand. Green materials-stabilized Pickering emulsion can potentially be used for oil/water separation. The NS washing agent displayed excellent pH- and Ca²⁺- responsiveness, generating transparent supernatants with low oil concentration and turbidity. Our work opens an interesting avenue for designing economical, high performance, and green washing agents.

Simultaneous removal of Zn2+ and p-nitrophenol from wastewater using nanocomposites of montmorillonite with alkyl-ammonium and complexant

Three types of alkyl-ammonium with different branching chains and three complexants with different functional groups were used to prepare alkyl-ammonium or complexant intercalated montmorillonite nanocomposite (A-Mt or C-Mt). In addition, synergistic intercalated montmorillonite nanocomposites (A/C-Mt) with alkyl-ammonium along with complexant were also prepared. The adsorption performance of the various nanocomposites toward Zn²⁺ and p-nitrophenol (PNP) from simulated binary wastewater containing both Zn²⁺ and PNP were systematically investigated. Characterization of Mt nanocomposites showed that both alkyl-ammoniums and complexants were successfully intercalated into the interlayers of Mt. The surfactant loading amounts of the various nanocomposites were also determined and correlated with the resulting expansion of the interlayer spacing. It was found that intercalation of alkane (OTAC) and -SH (CSH) were conducive to the adsorption of Zn²⁺ while -C₂H₄NH (TETA) and all alkyl-ammoniums were beneficial for PNP adsorption. The extent of adsorption was found to be controlled primarily by pH, i.e., the higher pH had a good effect on the adsorption of both Zn²⁺ and PNP. The adsorption process of Zn²⁺ onto Mt nanocomposites was more in line with the Freundlich model (R² = 0.99), while the Langmuir model described the adsorption of PNP well (R² = 0.99). The adsorption kinetics could be well described by the Elovich equation (R² = 0.98) and the double-constant model (R² = 0.89). Chemical adsorption was determined to be the dominant process between the contaminant and Mt nanocomposite surfaces.

Novel biochar and hydrochar for the adsorption of 2-nitrophenol from aqueous solutions: An approach using the PVSDM model

Two new adsorbents, namely avocado-based hydrochar and LDH/bone-based biochar, were developed, characterized, and applied for adsorbing 2-nitrophenol. The pore volume and surface diffusion model (PVSDM) was numerically solved for different geometries and applied to interpret the adsorption decay curves. Both adsorbents presented interesting textural and physicochemical characteristics, which achieved maximum adsorption capacities of 761 mg/g for biochar and 562 mg/g for hydrochar. The adsorption equilibrium data were well fitted by Henry isotherm. Besides, thermodynamic investigation revealed endothermic adsorption with the occurrence of electrostatic interactions. PVSDM predicted the adsorption decay curves for different adsorbent geometries at different initial concentrations of 2-nitrophenol. The surface diffusion was the main intraparticle mass transport mechanism. Furthermore, the external mass transfer and surface diffusion coefficients increased with the increase of 2-nitrophenol concentration.

Adsorption of two β-blocker pollutants on modified montmorillonite with environment-friendly cationic surfactant containing amide group: Batch adsorption experiments and Multiwfn wave function analysis

The novel environment-friendly hexadecanoamide propyltrimethy lammonium chloride (NQAS16-3) surfactant with different amounts (0.2, 0.4, 0.6, 0.8, 1.0, 1.2 CEC) was firstly used to modify montmorillonite, and the obtained organomontmorillonite (N-Mt) with the amount of surfactant equal to 1.0 CEC was utilized to adsorb two β-blocker pollutants- Atenolol (ATE) and acebutolol (ACE). The experimental results indicated that the equilibrium adsorption capacity of N-Mt(the organo-montmorillonite that the amount of modifier was 1.0 CEC) for ATE and ACE was 93.47 mg/g and 84.55 mg/g, respectively, which was more than twice that of raw montmorillonite for two pollutants, the adsorption was better fitted with the pseudo-second-order model and Langmuir isotherms model, and the adsorption was the spontaneous and exothermic process. Moreover, combining with the Zeta potential values of N-Mt, and with the help of Multiwfn wave function program based on density functional theory (DFT), the electrostatic interaction and the hydrophobic partitioning between N-Mt and two pollutant molecules were verified, p-π/π interaction between NQAS16-3 and ATE (or ACE) may be contributed to the increasing adsorption capacity of N-Mt for two β-blocker pollutants. The work provided novel organomontmorillonite for the removal of non-degradable β-blocker pollutants and the insight of the adsorption mechanism from the atomic level.

Geochemical and Physicochemical Characteristics of Clay Materials from Congo with Photocatalytic Activity on 4-Nitrophenol in Aqueous Solutions

This study investigated the geochemical and physicochemical characteristics of natural clay collected in the Democratic Republic of Congo. The optical properties of the sample collected in Golf (GOL) were tested in the removal of 4-nitrophenol in aqueous solution. The geochemical analysis depicted that all the samples are plotted within the shale quadrant. Furthermore, the Chemical Index of Alteration (CIA) indicated that the samples are extremely weathered. The particle size distribution ranged from 0.41 to 418.6 μm, while the pore diameters for all the samples were under 100 Å. A flake-like surface morphology was observed in all the samples. SiO₂, Al₂O₃, Fe₂O₃, K₂O, and TiO₂ were the major chemical compounds found in all the samples, while the XRD analysis showed the presence of quartz, kaolinite, magnetite, and illite. The presence of metal oxides (i.e., TiO₂ and Fe₂O₃) indicated that these natural clays can be used for photocatalytic oxidation of pollutants. The sample collected in Katuba (KAT) displayed the higher reflectance percentages for the selected wavelengths except at 200 nm. Interestingly, the GOL sample exhibited lower energy band gaps (2.68 and 3.94 eV) necessary for photocatalysis. The untreated GOL clay sample removed 99.13% of 4-nitrophenol from aqueous solution through the photodegradation process. The usage of the untreated GOL clay could be a cost-effective solution in the removal of 4-nitrophenol in wastewater.

Hydrophobic Cetyltrimethylammonium Bromide-Pillared Bentonite as an Effective Palm Oil Bleaching Agent

To promote a minimal use of acid in the activation of bentonite and to maintain oil quality during refinery and storage, a new class of bleaching agent, cetyltrimethylammonium bromide (CTAB)-pillared bentonite (CTAB@Bent), is fabricated. The influences of three independent intercalation variables, including temperature T (40, 50, and 60 °C), time t (2, 4, and 6 h), and CTAB loading m c (0.2, 0.25, 0.33, 0.50, and 1.00%, w/w), on the β-carotene removal rate are studied. The multilevel factorial design combined with the response surface methodology and three-way analysis of variance is employed to design and optimize experiments in regard to the three independent variables. Based on the optimization results, the highest β-carotene removal rate is monitored at 71.04% (w/w) using CTAB@Bent obtained at optimum intercalation conditions (CTAB@Ben-Opt): T = 40 °C, t = 3.2 h, m c = 1.00% (w/w). The mechanism study shows that the adsorption of β-carotene onto CTAB@Bent-Opt is spontaneous and endothermic, with the governing steps of physical interaction and ion exchange between β-carotene and the cationic head of CTAB. CTAB@Bent-Opt also exhibits characteristics superior to those of commercial raw bentonite and acid-activated bentonite, indicating that a more efficient β-carotene removal can be achieved using this new bleaching agent.

Strong influence of surfactants on virgin hydrophobic microplastics adsorbing ionic organic pollutants

Microplastic (MP) pollution has become an area of increasing concern because MPs accumulate various types of pollutants. Many previous studies have explored the interactions between MPs and hydrophobic pollutants. However, little research has been conducted on hydrophilic pollutants, which are of much higher concentration and ubiquitous in environment. Surfactants cause hydrophobic MPs to become hydrophilic, which may significantly enhance their capacities to adsorb hydrophilic pollutants. This study explored the influence of co-existing surfactants on the adsorption of ionic organic pollutants by MPs, and found that the presence of an ionic surfactant could significantly enhance the capacity of polyvinyl chloride (PVC, 0.2 mm) MPs to adsorb pollutants with opposite charges. The Langmuir methylene blue adsorption capacity of PVC could be increased from 172 to 4417 ppm in the presence of a sodium dodecyl benzene sulfonate surfactant. Nonionic surfactants impeded the adsorption of both cationic and anionic pollutants due to the steric resistance of the hydrophilic polyethelene glycol chains. The electrostatic interaction mechanism dominated the interfacial behaviors of ionic pollutants on surfactant-adsorbed MP interfaces. The effects of the surfactants were further verified using four different model pollutants and six surfactants. The adsorption capacities of real environmental MPs, including PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS), increased by three to twenty-six times. The adsorption properties of MPs may be determined by the presence of co-existing surfactants, rather than their polymer species or additives.

Nonlinear sorption of phenols and anilines by organobentonites: Nonlinear partition and space limitation for partitioning

Organobentonites, i.e., bentonites coated with surfactants such as cetyltrimethylammonium (CTAB), are superior and low-cost sorbents for removal of organic contaminants from wastewater. Nonlinear sorption of polar organic compounds such as phenols and anilines by organobentonites were widely observed and interpreted by adsorption mechanism. However, in this study, it was observed that the nonlinear sorption of phenols and anilines by CTAB coated bentonites (CTAB-bentonites) should be attributed to nonlinear partition mechanism with the additional space limitation in CTAB-bentonites for nonlinear partitioning, rather than adsorption mechanism. This nonlinear partition mechanism is supported by that (i) organobentonites is a partition medium, identified by the linear isotherms of polycyclic aromatic hydrocarbons (PAHs) and nitrobenzenes; (ii) sorption coefficients (logK_d), the ratio of adsorbed amount (q_e) to equilibrium concentration (C_e), and Dubinin-Ashtakhov (DA) model fitted sorption capacity (logQ⁰) of organic compounds, by a given CTAB-bentonite, are positively correlated with their octanol-water distribution coefficients (logK_OW) and solubility in octanol (logS_o) respectively; (iii) logK_d and logQ⁰ of a given organic compound by CTAB-bentonites are positively correlated with organic carbon contents (f_oc) of CTAB-bentonites, but not specific surface area. Specific interaction (i.e., hydrogen-bonding interaction), in addition to van der Waals force, is responsible for the nonlinear partitioning of phenols and anilines into CTAB-bentonites, because of the positively linear relationship between DA model fitted sorption affinity (E) and hydrogen-bonding donor parameter (α_m) of organic compounds. These results could help the recognizing of the nonlinear sorption behaviors of organic compounds by organobentonites and promote their environmental applications in wastewater treatment.

A char-clay composite catalyst derived from spent bleaching earth for efficient ozonation of recalcitrants in water

Catalytic ozonation is an efficient process that can be utilized to degrade recalcitrant organics. Char-clay composite derived from refinery spent bleaching earth (SBE) is an economical and readily available catalyst that can be used during the ozonation treatment of recalcitrants in wastewater. Four catalysts of SBE-N₂-650, SBE-N₂-850, SBE-O₂-650, and SBE-O₂-850 were prepared by heating the SBE at 650 and 850 °C under N₂ or O₂ conditions. High surface OH sites in the SBE-N₂-650 and SBE-O₂-650 relative to the SBE-N₂-850 and SBE-O₂-850 resulted in an increase in catalytic activity. Additional carbon (C), that existed in the SBE-N₂-650 and SBE-N₂-850, had a positive effect on catalytic activity. The SBE-N₂-650 exhibited the highest activity among those prepared catalysts. During catalytic ozonation, the SBE-N₂-650 increased the mineralization rate of benzoic acid by 36% when compared with single ozonation. Molecular ozone was decomposed at the surface active sites on SBE-N₂-650, generating active •OH, •O₂^-, or ¹O₂ species. Gas and liquid products having calorific values that are generated during SBE-N₂-650 preparation can be further utilized. This study introduces a potential use of SBE for the ozonation treatment of recalcitrant wastewaters.

Dinitrodiazophenol industrial wastewater treatment by a sequential ozone Fenton process

The ozonation process is efficient in degrading aromatic substances and substances with unsaturated bonds, but cannot effectively destroy small-molecule organic compounds, which accumulate. Likewise, the Fenton process is a classic wastewater treatment method, but requires strict pH control and produces secondary pollution when the concentration of organic substances is high. In this study, we applied a 1stO₃-2ndFenton sequential process to treat diazodinitrophenol (DDNP) industrial wastewater and provide suitable reaction conditions for Fenton process. For the 1stOzone process, organics removal increased as O₃ dosage increased. At optimized operation, the 1stO₃ process provided an acidic effluent (pH = 3) and reduced the organics concentration to a level suitable for the 2ndFenton process. Benzene ring substances as well as nitro group and diazo group compounds were greatly degraded in the 1stO₃ process and were further mineralized in the 2ndFenton process. Additionally, the biodegradability of DDNP industrial wastewater was greatly improved. This is the first reported time that ozonation and the Fenton process have been integrated sequentially to treat an explosive production wastewater. The study provides a feasible chemical oxidation method for treating DDNP industrial wastewater by simply combining two classic treatment processes.

Characterization and adsorption performance of graphene oxide - montmorillonite nanocomposite for the simultaneous removal of Pb2+ and p-nitrophenol

Montmorillonite-graphene oxide composite (MGC) with their own advantages was successfully fabricated for the simultaneous treatment of the combined pollution wastewater containing heavy metal ions and organic pollutants. The features of MGC were analyzed by X-ray diffraction, transmission electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy. Subsequently, a series of batch experiments were carried out to investigate the adsorption performance of Pb²⁺ and p-nitrophenol (PNP) onto MGC in single and binary system. The results indicated that MGC exhibited a gossamer layer with spots and a larger interlayer spacing. In single adsorption experiment, the removal of PNP by MGC reached 96.82%, while Pb²⁺ removal reached 98.94%, which was maintained at the same level as montmorillonite. In binary acidic system of Pb²⁺ and PNP, the removal of Pb²⁺ reached 98.23%, while PNP removal dropped to 51.06% due to their competitive adsorption. The thermodynamic study indicated that the chemisorption was predominant in the adsorption of Pb²⁺ onto MGC, while physisorption was for PNP. It was exactly that the strong competitiveness of Pb²⁺ brought the remarkable reduction in PNP adsorption capacity in the simultaneous adsorption.

Understanding Urea Encapsulation in Different Clay Minerals as a Possible System for Ruminant Nutrition

Considering the challenges of urea administration due to the high ureolytic activity of the rumen and the importance of its use, as well as taking into account the relevance of sustainably exploiting the technological potential of biodiversity, this research studies the encapsulation of urea in different clay minerals (palygorskite (Pal), sepiolite (Sep), and Veegum® (V)) as an alternative for use as nonprotein nitrogen (NNP) sources. A method of incorporation was developed in which the encapsulation of urea was proven by X-ray diffraction; fibrous materials, Pal and Sep had similar characteristics due to the decrease in the relative plane intensity (011), suggesting a decrease in the order of their stacking due to the presence of urea on the surface or inside channels. By contrast, V showed a 7.74° reflection shift, suggesting an increase in basal spacing from 11.45 Å in V to 14.88 Å in the sample after urea encapsulation. By thermogravimetry, it was observed that the presence of urea did not change the mass-loss profiles but only increased the percentage of loss in respective events, indicating urea incorporation in the clay minerals. These results provide a promising alternative for administering NNP sources in the ruminant diet.

Recyclable nanographene-based micromachines for the on-the-fly capture of nitroaromatic explosives

It has been more than a decade since nano/micromachines (NMMs) have received the particular attention of scientists in different research fields. They are able to convert chemical energy into mechanical motion in their surrounding environment. Herein, a powerful, efficient and fast strategy of using nanosized reduced graphene oxide flake (n-rGO)-based self-propelled tubular micromachines for the removal of nitroaromatic compounds (NACs) is described. This method relies on the integration of the rGO as a well-known adsorbent of aromatic compounds with chemically powered engines for the removal of explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol (TNP) and 2,4-dinitrotoluene (DNT). Nanographene oxide reduced electrochemically inside the pores of the polycarbonate membrane to form an outer layer (n-rGO, adsorbent layer) of the micromachines. Subsequent electrodeposition of nickel (Ni, magnetic layer) and platinum (Pt, catalytic layer) resulted in the formation of n-rGO/Ni/Pt micromachines. Notably, the bubble-propelled micromachines were able to remove nitroaromatic compounds with high efficiency (∼90-92%) compared to the efficiency of magnetic-guided (22-42%) and static (2.5-7%) micromachines. Most importantly, the micromachines were regenerated and reused several times. The regeneration is based on an electrochemical method in which electron injection into the machine causes the expulsion of contaminants from the outer layer of the micromachines within a few seconds. The integration of the powerful self-propulsion, high adsorbent capacity of rGO and the introduced ultrafast regeneration procedure are beneficial for the realization of an active platform for water remediation.

WITHDRAWN: An integrated approach towards sustainable wastewater treatment and biofuel production: A phytotechnological study on defatted residual seed biomass of Datura stramonium L

Available online 1 March 2019. This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

WITHDRAWN: A combinatorial bioinnovative approach integrating synthetic dye bioremediation and bioenergy production using waste pepper seed biomass

A combinatorial study integrating synthetic dye bioremediation and biodiesel production using discarded pepper seed biomass was performed for a cleaner and more sustainable environment/energy in the present work. The vegetal oil was extracted from the pepper seed biomass and the defatted residual biomass was mainly investigated as a sustainable green generation alternative biosorbent source for the treatment of colored aqueous effluents. To test the wastewater cleaning ability of biosorbent, basic red 46 was selected as a common harmful model synthetic dye. The kinetic, equilibrium and thermodynamic modeling studies were performed to elucidate the dye biosorption behavior of biosorbent. Besides, the performance of dye bioremediation system was evaluated using the kinetic modeling parameters, and for large scale dye purification applications, a single-stage batch bioreactor system was designed using the mathematical modeling data. The operating conditions significantly affected the biosorption process. The pseudo-second-order and Freundlich models provided the best fit to the kinetic and isotherm data, respectively. The thermodynamic studies showed that the dye biosorption was a feasible and spontaneous process. The maximum dye biosorption capacity of biosorbent based on Langmuir model was predicted as 82.019 mg g-1. As compared many other biosorbents reported in literature for the same contaminant, this high value revealed a great potential of biosorbent for the dye removal from aqueous medium. Thus, the present study showed that the discarded pepper seed biomass could be employed as a highly efficient as well as cost-effective material for both dye bioremediation and biodiesel production in a sustainable manner.

Bioremediation potential of waste biomaterials originating from coastal Zostera marina L. meadows for polluted aqueous media with industrial effluents

The studies on novel and efficient biosorbent materials for the promotion of environmental and economic sustainability have been become an up-to-date attempt by scientists for the removal of synthetic dyes from industrial effluents. The biosorbents prepared from biomass based resources are emerging as an alternative promising material for the environmental clean-up because of their low-cost, renewability, eco-friendly, easy availability and so forth characteristics. Hence, for the first time, the biosorption performance of abundantly available natural biowastes originating from coastal Zostera marina L. meadows was explored for the biotreatment of colored industrial effluents in the present study. The biosorption properties of biosorbent for methylene blue as a representative synthetic industrial dye were investigated by means of the operational parameters optimization, kinetic, isotherm, thermodynamic and characterization studies. The operating conditions significantly affected the biosorption process and the optimal values were determined as pH of 8, biosorbent dosage of 10 mg, dye concentration of 15 mg L^-1 and contact time of 120 min. Elovich and Freundlich models provided the best fit to the kinetic and isotherm data compared with other applied models, respectively. The negative change in free energy (-10.682 to -8.466 kJ mol^-1) indicated a thermodynamically feasible and spontaneous process. The characterization analysis showed that the biosorbent has appropriate chemical and physical properties for the dye biosorption. Thus, the present study displayed that the waste materials originating from coastal Z. marina L. meadows can be applied as a highly efficient as well as cost-effective green generation biosorbent for the clean-up of colored aquatic media.

Adsorption and regeneration of leaf-based biochar for p-nitrophenol adsorption from aqueous solution

As an environmentally friendly and low-cost adsorbent, biochar has great potential in wastewater treatment.

Synergistic degradation of PNP via coupling H2O2 with persulfate catalyzed by nano zero valent iron

Simultaneous activation of H₂O₂ and persulfate by nanoscaled Fe⁰ shows synergistic effect for degradation of p-nitrophenol with generating both hydroxyl and sulfate radicals in a wide initial pH range.

Reusable bentonite clay: modelling and optimization of hazardous lead and p-nitrophenol adsorption using a response surface methodology approach

In this work, bentonite clay (BC) calcined at 500 °C was used as an adsorbent (BC-500) for the adsorption of Pb²⁺ and p-nitrophenol.