Poly(trimesoyl chloride-melamine) grafted on palygorskite for simultaneous ultra-trace removal of methylene blue and toxic metals

Liquid-solid ratio during hydrothermal carbonization affects hydrochar application potential in soil: Based on characteristics comparison and economic benefit analysis

Returning straw-like agricultural waste to the field by converting it into hydrochar through hydrothermal carbonization (HTC) is an important way to realize resource utilization of waste, soil improvement, and carbon sequestration. However, the large-scale HTC is highly limited by the large water consumption and waste liquid pollution. Here, we propose strategies to optimize the liquid-solid ratio (LSR) of HTC, and comprehensively evaluate the stability, soil application potential, and economic benefits of corn stover-based hydrochar under different LSRs. The results showed that the total amount of dissolved organic carbon of hydrochars increased by 55.0% as LSR reducing from 10:1 to 2:1, while the element content, thermal stability, carbon fixation potential, specific surface area, pore volume, and functional group type were not obviously affected. The specific surface area and pore volume of hydrochar decreased by 61.8% and 70.9% as LSR reduced to 1:1, due to incomplete carbonization. According to the gray relation, hydrochar derived at LSR of 10:1 and followed by 2:1 showed greatest relation degree of 0.80 and 0.70, respectively, indicating better soil application potential. However, reducing LSR from 10:1 to 2:1 made the income of single process production increased from -388 to 968 ¥, and the wastewater generation decreased by 80%. Considering the large-scale application of HTC in fields for farmland improvement and environmental remediation, the comprehensive advantages of optimized LSR will be further highlighted.

Silver-assisted reduction of nitroarenes by an Ag-embedded curcumin/melamine-functionalized magnetic nanocatalyst

In the current study, we introduce a hybrid magnetic nanocomposite comprised of curcumin (Cur), iron oxide magnetic nanoparticles (Fe₃O₄ MNPs), melamine linker (Mel), and silver nanoparticles (Ag NPs). Initially, a facile in situ route is administrated for preparing the Fe₃O₄@Cur/Mel-Ag effectual magnetic catalytic system. In addition, the advanced catalytic performance of the nanocomposite to reduce the nitrobenzene (NB) derivatives as hazardous chemical substances were assessed. Nevertheless, a high reaction yield of 98% has been achieved in short reaction times 10 min. Moreover, the Fe₃O₄@Cur/Mel-Ag magnetic nanocomposite was conveniently collected by an external magnet and recycled 5 times without a noticeable diminish in catalytic performance. Therefore, the prepared magnetic nanocomposite is a privileged substance for NB derivatives reduction since it achieved notable catalytic activity.

Interface engineering of p-p Z-scheme BiOBr/Bi12O17Br2 for sulfamethoxazole photocatalytic degradation

The Z-scheme heterojunction has received widespread attention due to it can effectively improve the photocatalytic activity of photocatalytic materials. In this paper, a p-p Z-scheme hererojunction composed of bismuth oxybromide and oxygen-rich bismuth oxybromide was synthesized via facile one-step solvothermal method. Based on the characterization results, we demonstrated that the BiOBr/B_i12O₁₇Br₂ Z-scheme heterojunction was synthesized by intimate interface contact between BiOBr and B_i12O₁₇Br₂ p-type semiconductors. This endowed the heterojunction composite with excellent photogenerated carrier transfer ability and photogenerated electron-hole separation performance compared with pure BiOBr and B_i12O₁₇Br₂ materials, which were proven by photoelectrochemical measurement, photoluminescence spectra. The maximum photocurrent of BiOBr/Bi₁₂O₁₇Br₂ (≈0.32 μA) is approximately 3 times that of the original BiOBr (≈0.08 μA ) when light is irradiated. In addition, the BiOBr/B_i12O₁₇Br₂ p-p Z-scheme composite photocatalyst had good photocatalytic activity for sulfamethoxazole, with ·O₂^- free radicals as the main active species. It could photodegrade 99% sulfamethoxazole under light irradiation at 365 nm, and its degradation rate was approximately 13 times that of BiOBr and 1.5 times that of B_i12O₁₇Br₂ materials. Notably, BiOBr/B_i12O₁₇Br₂ exhibited an excellent performance after 4 consecutive runs. Besides, the possible degradation pathway of sulfamethoxazole was proposed. This work has reference significance for the construction of p-p Z-scheme heterojunctions and the treatment of environmental contaminants.

Efficient removal of humic acid in water using a novel TiO2 composite with biochar doping

Titanium dioxide modified with biochar (Ti–C) was prepared by a sol–gel method for the degradation of humic acid (HA) in aqueous solutions.

Adsorption of Hg(II) in solution by mercaptofunctionalized palygorskite

In the past 10 years, the treatment and restoration of soil and water bodies contaminated by mercury and other heavy metals have received unprecedented attention and support from China's environmental protection authorities. The search for low-cost and high-efficiency adsorbents has become one of the research hotspots in this field. In this paper, a simple and environment-friendly method was used to graft 3-mercaptopropyl trimethoxysilane on the surface of palygorskite. The synthesized mercaptofunctionalized palygorskite (M-PAL) was characterized by XRD, FT-IR, BET and SEM-EDS, respectively, and its adsorption conditions, adsorption models and thermodynamic parameters for Hg2+ were systematically investigated. The experimental results indicated that the saturated adsorption capacity of Hg2+ on the M-PAL could reach 203.4 mg·g-1, within 120 min at pH 4 and 298 K. By analyzing the experimental data of adsorption kinetics and thermodynamics, it was found that the adsorption process of Hg2+ conformed to the pseudo-second-order kinetic model, which belonged to chemical adsorption of the rate-controlled step; the Langmuir model better described the adsorption isotherm. The thermodynamic parameters obtained (ΔH=29.95 kJ·mol-1, ΔS=103.09 J·mol-1·K-1 and ΔG<0) show that the whole process is a spontaneous endothermic process. When the concentration of Na+, K+, Ca2+, Mg2+, Cl-, NO3-, H2C2O4 and C6H8O7 was 200 times that of Hg2+, although these organic acids had a slightly greater effect on the adsorption of Hg2+ on mercaptofunctionalized palygorskite than inorganic ions, the adsorption capacity remained above 185 mg·g-1. The adsorption products could be still stable in simulated acid rain with pH 3, 4, 5, 6, 7 and oxalic acid solution with concentration of 1, 2, 3, 4 and 5 mmol·L-1, and the desorption rates were about 3%. Through XPS analysis, the specific coordination of Hg2+ with the S atom on the surface of M-PAL was confirmed.

Fabrication of silane-modified magnetic nano sorbent for enhanced ultrasonic wave driven removal of methylene blue from aqueous media: Isotherms, kinetics, and thermodynamic mechanistic studies

In this study, we report a simple and economic one-pot synthesis of magnetite (Fe₃O₄) nanostructure and its modification with tetraethyl orthosilicate by coprecipitation method. The synthesized (Fe₃O₄@SiO₂) nano sorbent was applied for enhanced adsorptive removal of methylene blue by ultrasonic wave driven batch experiments. After successful synthesis, the nanostructure was characterized for their physical structure by FT-IR, VSM, TEM, and XRD. For the maximum adsorptive performance of nano sorbent, various parameters were optimized, such as dose, pH, time, concentration, and temperature. The adsorption mechanism was best fitted by Langmuir isotherm with a maximum capacity of 148.69 mg/g, while kinetics best fitted by pseudo-second-order kinetic. The synthesized nano sorbent was successfully applied for enhanced adsorptive removal of toxic methylene blue from aqueous media. The proposed method is promising and effective in terms of simplicity, cost operation, green energy consumption, reproducible, excellent reusability, and magnetically separability with fast kinetic.

Growth of binary anatase–rutile on phosphorylated graphene through strong P–O–Ti bonding affords a stable visible-light photocatalyst

Phosphorylated graphene sheets covalently bind, grow and stabilize biphasic anatase–rutile clusters through strong P–O–Ti bridges. The resulting nanocomposites stands as efficient visible-light photocatalysts for the degradation of dyes from water.

Graphitic carbon nitride-doped sewage sludge as a novel material for photodegradation of Eriochrome Black T

The bio-resource utilization of sewage sludge is presented by preparation of novel waste sludge-doped graphite carbon nitride (g-C₃N₄) photocatalyst. The sludge flocs which constitute bacteria and organic substances served as a pore-forming framework in the catalyst, while the inorganic fractions including those transition metals and crustal metals can function as dopants for sludge-based g-C₃N₄ composite. The physicochemical properties of as-prepared catalyst were well analyzed by multiple characterizations. The composite catalyst showed higher surface area (50 m²/g) and more mesoporous structures (8.9 × 10^-2 cm³/g) as compared with pristine g-C₃N₄ (8.4 m²/g and 6.6 × 10^-2 cm³/g, respectively). The photoelectrochemical results showed that introduced sewage sludge impurities lowered down the photocarriers recombination efficiency and enhanced more efficient electron-hole separation by about 100 times. The photocatalytic activity was tested by degradation of typical dye Eriochrome Black T (EBT). The optimal sample improved removal of EBT by 56% in 90 min under ultraviolet irradiation (λ = 254 nm). According to the results of main metal ion leaching concentration and reuse tests, the composite catalyst exhibited excellent stability and repeatability.

Highly Efficient Removal of Methylene Blue Dye from an Aqueous Solution Using Cellulose Acetate Nanofibrous Membranes Modified by Polydopamine

A new type of deacetylated cellulose acetate (DA)@polydopamine (PDA) composite nanofiber membrane was fabricated by electrospinning and surface modification. The membrane was applied as a highly efficient adsorbent for removing methylene blue (MB) from an aqueous solution. The morphology, surface chemistry, surface wettability, and effects of operating conditions on MB adsorption ability, as well as the equilibrium, kinetics, thermodynamics, and mechanism of adsorption, were systematically studied. The results demonstrated that a uniform PDA coating layer was successfully developed on the surface of DA nanofibers. The adsorption capacity of the DA@PDA nanofiber membrane reached up to 88.2 mg/g at a temperature of 25 °C and a pH of 6.5 after adsorption for 30 h, which is about 8.6 times higher than that of DA nanofibers. The experimental results showed that the adsorption behavior of DA@PDA composite nanofibers followed the Weber's intraparticle diffusion model, pseudo-second-order model, and Langmuir isothermal model. A thermodynamic analysis indicated that endothermic, spontaneous, and physisorption processes occurred. Based on the experimental results, the adsorption mechanism of DA@PDA composite nanofibers was also demonstrated.

A review on current practices and emerging technologies for sustainable management, sequestration and stabilization of mercury from gold processing streams

This paper presents an overview of unit processes that lead to potential mercury contamination during gold processing, which can pose serious health, environmental and technical concerns. Mercury release in gold processing streams is attributed to its dissolution from mercury bearing gold ores during cyanide leaching, and its mobile nature in the subsequent stages (e.g., carbon adsorption, elution, Zn precipitation/electrowinning, and smelting) and tailing storage facilities. Although retorting prior to smelting and sulphur-impregnated carbon filters have been developed to ensure minimal mercury contamination, these methods deal with gaseous mercury which is highly toxic and still a serious threat for both the environment and workers. Moreover, spent carbon filters containing high mercury concentrations introduce a new environmental issue. Therefore, there is a demonstrated need for safer and more efficient removal and sequestration techniques. Thus, this work includes a review of mercury removal from activated carbon as well as current mercury treatment and stabilization practices including precipitation, adsorption, cementation, ion exchange and solvent extraction. In addition, emerging mercury remediation materials such as nanomaterials and bimetals with a promising potential in sustainable management, sequestration, and stabilization of mercury from aqueous media will be highlighted. In summary, the results show a high mercury removal capacity of the outlined materials and techniques (between 70 to around 100% removal). However, one of the issues that emerges from these studies is the lack of selectivity of reagents for mercury capture from aqueous solutions containing precious metals. In this regard, future studies with more focus on the selective mercury removal from activated carbon, and then its precipitation from solutions using substances with a greater adsorption capacity to mass ratio (suitable for safe disposal), are therefore recommended.

Enhancing effects of activated carbon supported nano zero-valent iron on anaerobic digestion of phenol-containing organic wastewater

Activated carbon supported nano zero-valent iron material (NZVI/AC) was prepared and added to an anaerobic digestion tank to reduce the toxicity inhibition of phenols and increase the methane yield of phenol-containing organic wastewater (POW). The anaerobic digestion (AD) characteristics, including conversion rate of organic substances, removal rate of phenol, and methane yield of POW with different concentrations of phenol were studied, and moreover, the enhancing effects of NZVI/AC on the AD of POW were focused. When the concentration of phenol was below 500 mg/L, the methane yield from AD of POW was 387.5 mL, which was 10.71% higher than that from control organic water without phenol, however, phenol concentrations greater than 1000 mg/L severely inhibited AD, and methane yield was only 50% of the control sample. Indicating that anaerobic microorganisms had a certain degree of tolerance to phenol, and low concentration of phenol could promote AD of organic water although the phenol with high concentration showed severe inhibition. The methane yield increased due to the probable conversion of phenol to methane by microbial actions. In the AD of POW with 500 mg/L phenol, the conversion rate of organic substances increased from 37.49% (control group without any accelerant) to 66.56% after adding NZVI/AC. The removal rate of phenol also increased from 39.03% to 81.32%. Cumulative methane yield increased by 145.5%-810 mL compared with the control group. The AC carrier in NZVI/AC exerted a good adsorption effect on phenols, reducing the concentration of phenols in the solution and thus minimizing their toxic effects on microbial activity. The NZVI loaded on AC particles strengthened the electron transfer between methanogens by its good electrical conductivity, and then promoted the AD performance of organic matter. Furthermore, NZVI exerted a micro-electrolytic effect on phenolic substances, which could increase the removal rate of phenol. Therefore, NZVI/AC could be used as an efficient accelerant for the AD of POW to enhance the AD process.

One-pot green synthesis of polymeric nanocomposite: Biodegradation studies and application in sorption-degradation of organic pollutants

The research work proposes the synthesis of a nanocomposite hydrogel which is a dual combination of binary interpenetrating network (BIPN) and bismuth ferrite nanoparticles. BIPN synthesized from binary graft copolymer (BGC) used as starting material. The cross-linked network of BGC is interpenetrating the newly synthesized cross-linked network of poly(acrylic acid) and the product is named as BIPN. Binary graft copolymer had been synthesized from grafting of guggul aqueous extract with copolymeric chains of acrylamide (primary monomer) and acrylic acid (secondary monomer) crosslinked by N,N'-methylene bisacrylamide (MBA). The maximum percentage swelling was evaluated for BGC through optimization of various reaction parameters: amount of water, binary ratio of acrylamide to acrylic acid, concentrations of MBA, ammonium persulphate, pH, temperature and time. Considering pre-optimized parameters for BGC synthesis, BIPN formation required optimization of only acrylic acid. Maximum percentage swelling obtained was 1497.79% and 308.15% for BGC and BIPN, respectively. Maximum percentage biodegradation of 90.64% and 82.38% were calculated for BGC and BIPN, respectively using composting method. Degradation efficiency of brilliant blue (BB) and fuchsin basic (FB) dyes was in the order: Nanocomposite ≫ BIPN > BGC. Maximum percentage degradation observed in case of nanocomposite was 94.1% and 99.3% in sunlight for BB and FB, respectively. The interaction of dyes with the nanocomposite involved mainly ionic interactions. The adsorption models Freundlich and Langmuir were applicable to overall adsorption and degradation process of BB and FB, respectively. Maximum adsorption capacities corresponding to minimum concentration i.e. 10 mg L^-1 for BB and FB were calculated as 0.409 mg g^-1 and 0.439 mg g^-1, respectively. Second order and first order kinetics were found to be suitable for BB and FB adsorption-degradation pathways, respectively. Intraparticle diffusion mechanism was favorable to both dyes and adsorption followed three steps. Gas chromatography coupled with mass spectrometric analysis could give the degraded products which was helpful in drawing degradation pathway. The degradation process involved active radical species (O₂^-., OH^.) and they carry out oxidation-reduction reactions on dyes to give decolorized solution containing mineral ions.

Populus tremula, Nerium oleander and Pergularia tomentosa seed fibers as sources of cellulose and lignin for the bio-sorption of methylene blue

Cellulose-based substrates could represent potential funds for the sorption of pollutants. Herein, methylene blue was selected for demonstrating the bio-sorption efficiency of Nerium oleander, Pergularia tomentosa and Populus tremula seed fibers. Their cellulose contents were 45%, 43.8% and 60%. Their lignin amounts were 21%, 8.6% and 12%, respectively. Fourier Transform InfraRed suggested that the interaction of these bio-products with methylene blue could occur between hydroxyl and ester groups of cellulose and lignin and the sulfur and nitrogen atoms of the dye. Scanning Electron Microscopy showed a swelling of the bio-matters after dye biosorption. From X-Ray Diffraction, the shifting for higher values of the peaks related to the amorphous phase indicated the establishment of new rearranged regions. Such change from the decomposition behavior event studied by Thermogravimetric Analysis/Differential Thermal Analysis revealed that methylene blue was interacted with cellulose and lignin structures. The effect of adsorbent dosage, pH, time, dye concentration and temperature was investigated in controlled batch experiments. Excellent sorption capacities followed the order: Nerium oleander (280.2 mg g^-1) > Populus tremula (168 mg g^-1) > Pergularia tomentosa (145.3 mg g^-1). Freundlich fitted best the equilibrium data suggesting cooperative interactions via physisorption and chemisorption phenomenon. Kinetic data complied well with the pseudo-second-order suggesting a chemisorption mechanism.