Recycling Spent Cr Adsorbents as Catalyst for Eliminating Methylmercaptan

Cutting-edge regeneration technologies for saturated adsorbents: a systematic review on pathways to circular wastewater treatment system

Adsorption seemed like an excellent physicochemical process employed for wastewater treatment. In the last few decades, significant improvements have been made in efficiency and economy to remove contaminants from wastewater using several adsorbents. However, less attention was paid to the regeneration of used adsorbents. Aside from the adsorbent's high adsorption performance, the disposal of spent adsorbents is an environmental concern. Regeneration is an important aspect to stimulate the adsorption efficiency of the spent adsorbent for wastewater treatment. This article reviews the various regeneration techniques like electrochemical regeneration, biological regeneration, thermal regeneration, ultrasound regeneration, and chemical regeneration in detail that have been performed for the renewal of saturated adsorbents. In the ultrasonic regeneration technique, Fe3O4-loaded coffee waste hydrochar adsorbent showed 100% regeneration efficiency (RE) after 1.3 h at the power consumption of 300 W/L. Electrochemical regeneration of granular activated carbon, Nyex, graphene and titanium dioxide composite, and Nyex 1000 showed 100% RE after 3, 0.16, 0.12, and 1.5 h, respectively, with electrolyte Na2SO4 and NaCl. In the regeneration technique, powdered activated carbon showed 90% RE after 48-72 h. Immobilized fungal biomass (Rhizopus nigricans) adsorbent showed 111-115% RE with base (0.01 N NaOH, NaHCO3, and Na2CO3) solvent. The present study addresses issues including waste generation, adsorbent potential and efficiency, eco-friendly techniques, and the release of adsorbed pollutants in regenerating saturated adsorbents. The mechanisms of adsorbent regeneration were thoroughly examined, highlighting the significance of the regeneration process in adsorption. Furthermore, this review discusses the advantages of hybrid regeneration techniques like microwave-activated ultraviolet-advanced oxidation, electro-peroxide approach, electrochemical and electrothermal methods, and the secondary use of spent adsorbents as catalysts, fertilizer, cementitious materials, secondary adsorbent bio-fuels, etc. Using saturated adsorbents is a practical technology for sustainable wastewater treatment that has the potential to minimize pollution and promote a circular economy. This review concludes with a discussion of the present challenges in the regeneration of the used adsorbents, as well as future directions for ensuring the system's feasibility from an economic and environmental standpoint for use on an industrial scale.

Disentangling activity-stability trade-off in the catalytic degradation of malodorous sulfur-containing VOCs driven by active sites' self-dynamic evolution

The catalytic degradation of malodorous sulfur-containing volatile organic compounds (S-VOCs), especially methanethiol (CH3SH), faces an enormous challenge in striking a balance between activity and stability. Herein, we develop the time-tandem and spatial-extended strategy for synthesizing t-MoO3/meso-SiO2 nano-reactor-type catalysts and reveal the migration and transformation behaviors of both carbon and sulfur species at the mesoscopic scale to break the catalytic CH3SH activity and stability trade-off. The dynamic evolution of active centers from initial oxygen sites and acid sites to sulfur vacancies in MoS2 during the reaction process as well as the formation of a new dimethyl disulfide (CH3SSCH3) reaction pathway are identified as the main reason for the catalysts' superior activity and sulfur resistance. H2-TPR, XPS, Raman spectroscopy and other characterizations suggested that the final deactivation is transformed from the conventional sulfide and sulfate poisoning mechanism to MoS2 active phase destroying mechanism. Extending the micropore to mesopore also contributes to the high sulfur-resistance stability due to the greater ability to accommodate deposited elemental sulfur. Furthermore, t-MoO3/meso-SiO2 catalysts have confirmed the excellent performance in the catalytic degradation of dual-component thiols and CH3SH with water vapor present in the realistic environment, also substantiating its wide application potential in the catalytic degradation of S-VOCs.

Structural/surface characterization of transition metal element-doped H-ZSM-5 adsorbent for CH3SH removal: identification of active adsorption sites and deactivation mechanism

CH3SH is a potential hazard to both chemical production and human health, so controlling its emissions is an urgent priority. In this work, a series of transition metal-loaded H-ZSM-5 adsorbents (Si/Al = 25) (Cu, Fe, Co, Ni, Mn, and Zn) were synthesized through the wet impregnation method and tested for CH3SH physicochemical adsorption at 60 °C. It was shown that the Cu-modified H-ZSM-5 adsorbent was much more active for CH3SH removal due to its abundant strong acid sites than other transition metal-modified H-ZSM-5 adsorbents. The detailed physicochemical properties of various modified H-ZSM-5 adsorbents were characterized by SEM, XRD, N2 physisorption, XPS, H2-TPR, and NH3-TPD. The effects of metal loading mass ratio, calcination temperature, and acid or alkali modification on the performance of the adsorbent were also investigated, and finally 20% Cu/ZSM-5 was found to have the best adsorption capacity after calcined at 350 °C. Additionally, the Cu/ZSM-5 adsorbent modified by sodium bicarbonate could expose more active components, which improved the adsorbent's stability. However, the consumption and reduction of the active component Cu2+ and the accumulation of sulfate during the adsorption process are the main reasons for the deactivation of the adsorbent. In addition, the simultaneous purging of N2 + O2 can effectively restore the adsorption capacity of the deactivated adsorbent and can be used as a potential strategy to regenerate the adsorbent.

Covalent organic framework modified vermiculite for total Cr removal and subsequent recycling for efficient ciprofloxacin and NO photooxidation

Design and fabrication of feasible remediation composites for total Cr (Cr(T)) removal is still challenging but urgently required. Herein, eco-friendly expanded vermiculite (VE) is integrated with a photoactive covalent organic framework (COF) polymer, in which photoinduced electrons of surface anchored COF can freely transfer to Cr(VI) for chemical reduction, and layered expanded VE allows ion exchange between resultant Cr(III) cations and interlayered K+, Ca2+, Mg2+, Na+, etc. The Cr(T) removal capacities of the surface-modified VE with important parameters (solution pH value, initial Cr(VI) concentration, etc.) are discussed extensively to understand how to select the best conditions for optimum Cr(T) removal performance. More interestingly, from a circular economy view point, spent Cr-loading VE-based waste can serve as a photocatalyst towards oxidation conversion of ciprofloxacin and NO gas subsequently. Explanations for different effects on physicochemical properties as well as catalytic activities of the reused Cr-loading waste are given. This strategy could provide valuable and promising contribution towards the development of sustainable low-cost mineral materials for Cr(T) removal. These findings also shed new light on the research of recycling spent photocatalyst for resource and reutilization.

Low-temperature biochar production from torrefaction for wastewater treatment: A review

Biochar, a carbon-rich and por ous material derived from waste biomass resources, has demonstrated tremendous potential in wastewater treatment. Torrefaction technology offers a favorable low-temperature biochar production method, and torrefied biochar can be used not only as a solid biofuel but also as a pollutant adsorbent. This review compares torrefaction technology with other thermochemical processes and discusses recent advancements in torrefaction techniques. Additionally, the applications of torrefied biochar in wastewater treatment (dyes, oil spills, heavy metals, and emerging pollutants) are comprehensively explored. Many studies have shown that high productivity, high survival of oxygen-containing functional groups, low temperature, and low energy consumption of dried biochar production make it attractive as an adsorbent for wastewater treatment. Moreover, used biochar's treatment, reuse, and safe disposal are introduced, providing valuable insights and contributions to developing sustainable environmental remediation strategies by biochar.

Catalysts for gaseous organic sulfur removal

Organic sulfur gases (COS, CS₂ and CH₃SH) are widely present in reducing industrial off-gases, and these substances pose difficulties for the recovery of carbon monoxide and other gases. The reaction pathways and reaction mechanisms of organic sulfur on different catalyst surfaces have yet to be fully summarized. The literature shows that many factors, such as catalyst synthesis method, loaded metal composition, number of surface hydroxyl groups, number of acid-base sites and methods of surface modification, have important effects on the catalytic performance of metal catalysts. Therefore, this paper presents a comprehensive review of the research on the application of catalysts such as zeolites, metal oxides, carbon-based materials, and hydrotalcite-like derivatives in the field of organic sulfur removal. Future research prospects are summarized, more in situ characterization experiments and theoretical calculations are needed for the catalytic decomposition of methanethiol to analyze the coke generation pathways at the microscopic level, while the simultaneous removal of multiple organic sulfur gases needs to be focused on. Based on previous catalyst research, we propose possible innovations in catalyst design, desulfurization technology and organic sulfur resource utilization technology.

Sustainable conversion of saturated adsorbents (SAs) from wastewater into value-added products: future prospects and challenges with toxic per- and poly-fluoroalkyl substances (PFAS)

Following circular economy principles, the reuse or recycling of saturated adsorbents (SAs or adsorbate-laden adsorbents) into a low-cost engineered product is a valuable alternative to eliminate secondary pollution after adsorption. This review evaluates the application of SAs for the generation of products that can serve as (i) antimicrobial agents or disinfectants, (ii) materials for civil construction, (iii) catalysts, (iv) fertilizers, and (v) secondary adsorbents. The importance of SAs configuration in terms of functional groups, surface area and pore morphology played a crucial role in their reutilization. The SAs-laden silver ions (Ag⁺) strongly inhibit (~ 99%) the growth of Escherichia coli and Staphylococcus aureus microbes found in drinking and wastewaters. The intra-solidification of SAs containing toxic metal pollutants (As³⁺ and F^-) with cementitious materials can effectively reduce their leaching below permissible limits of USEPA standards for their utility as additives in construction work. The existence of transition metal ions (Cu²⁺, Cr^3+/6+, Ni²⁺) on the surface of SAs boosted activity and selectivity towards the desired product during catalytic oxidation, degradation, and conversion processes. The thermally recycled SAs can assist in the secondary adsorption of pollutants from another waste solution due to a larger surface area (> 1000 m²g^-1). However, there are chances that the SAs discussed above will contain traces of PFAS. The article summarizes the challenges, performance efficacy, and future prospects at the end of each value-added product. We also highlight critical challenges for managing PFAS-laden SAs and stimulate new perspectives to minimize PFAS in air, water, and soils.

Unraveling the Synergistic Reaction and the Deactivation Mechanism for the Catalytic Degradation of Double Components of Sulfur-Containing VOCs over ZSM-5-Based Materials

The competitive adsorption behavior, the synergistic catalytic reaction, and deactivation mechanisms under double components of sulfur-containing volatile organic compounds (VOCs) are a bridge to solve their actual pollution problems. However, they are still unknown. Herein, simultaneous catalytic decomposition of methyl mercaptan (CH3SH) and ethyl mercaptan (C2H5SH) is investigated over lanthanum (La)-modified ZSM-5, and kinetic and thermodynamic results confirm a great difference in the adsorption property and catalytic transformation behavior. Meanwhile, the new synergistic reaction and deactivation mechanisms are revealed at the molecular level by combining with in situ diffuse reflectance infrared spectroscopy (in situ DRIFTS) and density functional theory (DFT) calculations. The CH3CH2* and SH* groups are presented in decomposing C2H5SH, while the new species of CH2*, active H* and S*, instead of CH3* and SH*, are proved as the key elementary groups in decomposing CH3SH. The competitive recombining of SH* in C2H5SH with highly active H* in dimethyl sulfide (CH3SCH3), an intermediate in decomposing CH3SH, would aggravate the deposition of carbon and sulfur. La/ZSM-5 exhibits potential environmental application due to the excellent stability of 200 h and water resistance. This work gives an understanding of the adsorption, catalysis, reaction, and deactivation mechanisms for decomposing double components of sulfur-containing VOCs.

Review on biopolymers and composites - Evolving material as adsorbents in removal of environmental pollutants

The presence of pollutants and toxic contaminants in water sources makes it unfit to run through. Though various conventional techniques are on deck, development of new technologies are vital for wastewater treatment and recycling. Polymers have been intensively utilized recently in many industries owing to their unique characteristics. Biopolymers resembles natural alternative to synthetic polymers that can be prepared by linking the monomeric units covalently. Despite the obvious advantages of biopolymers, few reviews have been conducted. This review focuses on biopolymers and composites as suitable adsorbent material for removing pollutants present in environment. The classification of biopolymers and their composites based on the sources, methods of preparation and their potential applications are discussed in detail. Biopolymers have the potentiality of substituting conventional adsorbents due to its unique characteristics. Biopolymer based membranes and effective methods of utilization of biopolymers as suitable adsorbent materials are also briefly elaborated. The mechanism of biopolymers and their membrane-based adsorption has been briefly reviewed. In addition, the methods of regeneration and reuse of used biopolymer based adsorbents are highlighted. The comprehensive content on fate of biopolymer after adsorption is given in brief. Finally, this review concludes the future investigations in recent trends in application of biopolymer in various fields in view of eco-friendly and economic perspectives.

Potential applications of spent adsorbents and catalysts: Re-valorization of waste

Water pollution has increased with the growth of human population and its industrial activities. Textile effluents constitute a particular threat due to the presence of heavy metals and dyes. Adsorption is one of the most applied technologies in contaminant removal owing to its high efficiency, low cost, practical implementation and possibility to operate in several experimental conditions. However, this process implies the generation of spent materials, representing a limitation to scale-up. Although the applications of exhausted solids in effluent treatments have not been extensively reviewed before, their reutilization appears to be an environmentally and economically attainable alternative. This work summarizes the potential value of solids post-use. The open literature reports that spent adsorbents based on polysaccharides with iron oxides may adsorb up to 1 g g^-1 of organic pollutants and up to near 100% of metallic ions from wastewater (Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺). The studied conditions vary from 30 to 60 °C, 0,05 to 6 g L^-1 of adsorbent, 10 mg L^-1 to 250 mg L^-1 of organic pollutants (dyes) and pH between 2 and 8. Spent adsorbents in dye removal have proven to have near 95% efficiency in metallic ion adsorption. Otherwise, the spent solids could be applied to remove Ca²⁺ and Mg²⁺ to decrease the hardness of water. Furthermore, at the end-of-life, these materials could be used in cement and ceramic production. To achieve these aims, it is necessary to design the bioadsorbents and biocatalysts considering not only their primary uses (as adsorbent of organic pollutants), but also secondary applications (as toxic metal or hardness removal) and even their final destination (as additive in ceramic or cement production). Finally, further studies are required on the composition, properties, stability at long-term and the life-cycle cost of these materials when they are applied in the construction industry.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

Loading with micro-nanosized α-MnO2 efficiently promotes the removal of arsenite and arsenate by biochar derived from maize straw waste: Dual role of deep oxidation and adsorption

The function of biochar (BC) as an eco-friendly adsorbent for environmental remediation is gaining much attention. However, the pristine BC had limited abilities for the removal of As (III, V). Towards this issue, this study synthesized biochar/micro-nanosized α-MnO₂ (BM) composites with different mass ratios of biochar to MnO₂. Comprehensive characterizations confirmed the successful loading of micro-nanosized α-MnO₂ onto the BC surface and the obvious specific surface area enhancement (7.5-13.5 times) of BM relative to BC. BM composites exhibited 5.0-13.0 folds higher removal capacity for As (III, V) than pristine BC since the composites gave full play to the oxidation contributed by micro-nanosized α-MnO₂ substrate and adsorption functions provided by the Mn-OH, BC-COOH, and BC-OH functional groups. Moreover, BM was well reused maintaining a relatively high removal efficiency for As (III, V). Regardless of reaction time and initial As (III) concentration (C₀), the removal of As (III) by pristine BC was negligibly contributed by the oxidized As (V) remaining in solutions, with the relative contribution <15.0%. For the BM composites, relative contribution of adsorbed As (III, V) dominated over that of oxidation to mobile As (V) remaining in solution, and exhibited the decreasing trend with increasing C₀. These findings demonstrated BM as a promising candidate in remediating As (III, V)-polluted water, and provide mechanistic insights into the role of oxidation and adsorption in As (III, V) removal.

Toxic chromium treatment induce amino-assisted electrostatic adsorption for the synthesis of highly dispersed chromium catalyst

Removal of toxic Cr (VI) from aqueous solutions using silicon-based adsorbents has been widely investigated. Meanwhile, contradictory between highly dispersed active Cr species and high Cr loading over commercial Cr-based catalyst was inevitable. In this work, amino-assisted electrostatic adsorption from toxic Cr (VI) treatment was developed to prepare highly dispersed Cr oxides catalysts supported on MCM-41. The Cr loading was as high as 15 wt%, and structure characters of the catalysts were well-reserved. As a result, electrostatic adsorption and subsequent complexation from negatively charged Cr (VI) species and positively charged ammonium groups made a positive contribution to the appearance of highly dispersed mono Cr species, which gave rise to improved non-oxidative propane dehydrogenation (PDH) activity. In contrast, the agglomeration of Cr species and lower PDH activity were observed on the sample synthesized using the traditional wet impregnation method. Besides, the transformation of Cr (VI) to active Cr (III) sites over the catalyst was proved by the designed in-situ H₂-TPR, ex-situ UV-vis and Raman spectra results. This procedure reflects a new avenue of green chemistry, which can recycle waste Cr adsorbents as efficient PDH catalysts.

Carbohydrate biopolymers, lignin based adsorbents for removal of heavy metals (Cd2+, Pb2+, Zn2+) from wastewater, regeneration and reuse for spent adsorbents including latent fingerprint detection: A review

Living organisms are created by carbohydrate biopolymers such as chitosan, carboxymethyl cellulose, alginate and lignin. These carbohydrate biopolymers have been extensively used for environmental applications because they are bio-degradable, bio-compatible, non-toxic and inexpensive. Recently, carbohydrate biopolymers have been used to prepare different nanocomposite adsorbents for treatment of wastewater. These adsorbents explored the removal effectiveness of inorganic pollutants from aqueous solution. This review article discusses the synthesis and application of chitosan, carboxymethyl cellulose, alginate and lignin nanocomposites as adsorbents for heavy metals. Toxic metals can be efficiently absorbed by cross-linkers, distributed in aqueous solutions of divalent heavy metal ions to examine their polymer absorption capacity. These nanocomposites were used for the adsorption of highly toxic metals such as Cd2+, Pb2+ and Zn2+ in water. To make heavy metal ion uptake more effective, more functionalization has been implemented such as blending, grafting, or mixing with different nanomaterials with an extra functional group. The integration of the second part into the main polymer chain not only adds functionality but also increases mechanical efficiency, one of the core criteria for adsorbent recyclability. The remediation method of metal ions from wastewater is cheaper as long as the adsorbent is reused. Furthermore, they exhibited good performance for the reuse of spent adsorbents after adsorption-desorption processes including latent fingerprint detection with nanomaterials by using the powder dusting method. Chitosan, carboxymethyl cellulose, alginate and lignin based nanocomposites have demonstrated better adsorption activities due to great physical and chemical properties for the chelation of heavy metals such as Cd2+, Pb2+ and Zn2+ from water and also higher regeneration with various eluents after several desorption-adsorption cycles. In addition, reuse of the spent adsorbents in latent fingerprint detection with different nanomaterials is discussed. Finally, this review article makes recommendations for future studies in light of environmentally favourable and economical applications.

Promotional Effects of Rare-Earth Praseodymium (Pr) Modification over MCM-41 for Methyl Mercaptan Catalytic Decomposition

Praseodymium (Pr)-promoted MCM-41 catalyst was investigated for the catalytic decomposition of methyl mercaptan (CH3SH). Various characterization techniques, such as X-ray diffraction (XRD), N2 adsorption–desorption, temperature-programmed desorption of ammonia (NH3-TPD) and carbon dioxide (CO2-TPD), hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectrometer (XPS), were carried out to analyze the physicochemical properties of material. XPS characterization results showed that praseodymium was presented on the modified catalyst in the form of praseodymium oxide species, which can react with coke deposit to prolong the catalytic stability until 120 h. Meanwhile, the strong acid sites were proved to be the main active center over the 10% Pr/MCM-41 catalyst by NH3-TPD results during the catalytic elimination of methyl mercaptan. The possible reaction mechanism was proposed by analyzing the product distribution results. The final products were mainly small-molecule products, such as methane (CH4) and hydrogen sulfide (H2S). Dimethyl sulfide (CH3SCH3) was a reaction intermediate during the reaction. Therefore, this work contributes to the understanding of the reaction process of catalytic decomposition methyl mercaptan and the design of anti-carbon deposition catalysts.

The identification of active chromium species to enhance catalytic behaviors of alumina-based catalysts for sulfur-containing VOC abatement

As to the treatment of sulfur containing VOCs (examples are compounds of CH₃SH and C₂H₅SH), finding a catalyst with high performance is necessary. In this work, Cr_(x)-Al₂O₃ (x = 1.0, 2.5, 5.0, 7.5 and 10 wt%) catalysts were synthesized, and their behaviors toward CH₃SH and C₂H₅SH abatement were investigated. The results indicated that Cr_(7.5)-Al₂O₃ exhibited higher activity than other samples and the reported catalysts, on which CH₃SH could be almost completely converted at 375 °C, while the temperature for the reported catalysts was above 450 °C. Moreover, there was no obvious deactivation during 30 h on stream over Cr_(7.5)-Al₂O₃, while only about 10 h was found on the reported CeO₂ and HZSM-5 catalysts. The improvement in the catalytic performance could be explained by the important role of the Cr⁶⁺ species, while the state of Cr³⁺ was suggested to be ineffective in the degradation process. The identification of the active Cr sites was proved by the characterization measurements, and the control experiments by using mechanical mixtures of CrO₃ or Cr₂O₃ with Al₂O₃ as well as the comparison studies between spent Al₂O₃ and spent Cr_(7.5)-Al₂O₃ catalysts.

Microwave-Assisted Synthesis of trans-Cinnamic Acid for Highly Efficient Removal of Copper from Aqueous Solution

trans-Cinnamic acid was synthesized under microwave irradiation, and it was used for the removal of copper, a toxic metal found in industrial wastewater, from synthetic polluted aqueous solutions. Copper removal is more favorable at pH 5 and was enhanced by increasing the copper initial concentration, reaching a maximum uptake capacity of 389.5 mg/g, which is higher than those reported in the literature. Temperature exhibited a negligible effect on the removal of copper by trans-cinnamic acid. The isotherm equilibrium uptake data were found to be described by the Langmuir model. In addition, the study of the removal kinetics shows that the uptake of copper by trans-cinnamic acid follows pseudo-first order kinetics, and equilibrium is attained at approximately 30 min. Based on the X-ray photoelectron spectroscopy, X-ray diffraction, scanning transmission electron microscopy, and Fourier-transform infrared spectroscopy studies, a copper-cinnamic acid complex [Cu(CA)2] is formed during the removal process. The reusability of this coordination compound was investigated using HCl, HNO3, and NaOH 0.1 M as desorption eluents; HCl was capable of completely desorbing copper from [Cu(CA)2], and trans-cinnamic acid was recovered as the trans-isomer. Alternatively, the [Cu(CA)2] was used to remove octamethylcyclotetrasiloxane from gaseous streams for biogas purification, obtaining an adsorption capacity of 3.37 mg/g. These promising results demonstrate the feasibility of copper removal by trans-cinnamic acid because of its high uptake capacity and potential reusability.

Functionalized magnetic mesoporous silica/poly(m-aminothiophenol) nanocomposite for Hg(II) rapid uptake and high catalytic activity of spent Hg(II) adsorbent

Currently, magnetic mesoporous silica nanospheres have been employed widely as adsorbents due to their large surface area and easy recovery. Herein, the functionalized magnetic mesoporous silica/organic polymers nanocomposite (MMSP) was fabricated by the grafted poly(m-aminothiophenol) embedded the aminated magnetic mesoporous silica nanocomposite based on Fe₃O₄ magnetic core, which was shelled by mesoporous silica and further modified by (3-aminopropyl) triethoxysilane. The adsorption properties of as-developed MMSP were systematically explored by altering the experimental parameters. The results indicated that the adsorption capacity and removal percentage of the MMSP could reach 243.83 mg/g and 97.53% within only 10 min at pH 4.0, and the coexisting ions had no significant effect on the selective Hg(II) ions removal from aqueous solutions, meanwhile, the adsorbent recovered by a magnet still exhibited good adsorption performance after recycled 5 times. In addition, by analyzing experimental data, the adsorption process of Hg(II) ions belonged to spontaneous exothermic adsorption, and the possible adsorption mechanisms were proposed based on the pseudo-second-order model and Langmuir model. After adsorption study, the waste material adsorbed Hg(II) was developed as an efficient catalyst for transformation of phenylacetylene to acetophenone with yield of 97.06%. In this study, we designed an efficient and selective material for Hg(II) ions remove and provided a treatment of the post-adsorbed mercury adsorbent by converting the waste into an excellent catalyst, which reduced the economic and environmental impact from conventional adsorption techniques.

Microwave assistant rapid synthesis MCM-41-NH2 from fly ash and Cr(VI) removal performance

Synthesis of silicon materials from fly ash is an ecologically justified process aimed at the transformation of energy sector waste-fly ash into mesoporous silicon material of broad possible application field. In this study, the MCM-41-NH₂ was successfully synthesized from industrial solid waste fly ash via a facile and fast process of alkali fusion method under the assistant of microwave. Due to the employ of microwave, the aging time was controlled within 30 min, which was significantly shorter than that of traditional hydrothermal method (48-72 h). And, the obtained MCM-41-NH₂ was shown an excellent performance to remove Cr(VI) from solution under the investigation of fixed-bed column. The maximum adsorption capacity for Cr(VI) was 53.77 mg/g. Additionally, the effect of initial concentration, flow rate, bed height, and pH on Cr(VI) removal were investigated, and the models of Thomas and Adams-Bohart were applied to predict the experiment data; the correlation coefficients (R²) of Thomas model under the investigated conditions were all close to 1. Furthermore, the adsorbent was characterized by N₂ adsorption-desorption isotherm, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and NH₃-Temperature Programmed Desorption (NH₃-TPD). The results showed that amino groups play an important role in the adsorption process. Cr(VI) was firstly adsorbed on the surface of the MCM-41-NH₂, and then some of the adsorbed Cr(VI) were reduced to Cr(III) by the release of the protons of the ammonium. The information showed that MCM-41-NH₂ could be an effective and low-cost sorbent for removing Cr(VI) from wastewater. Furthermore, recycling experiments showed that the spent adsorbent had high catalytic performance for methyl mercaptan (CH₃SH). Graphical abstract .

Triphenylamine Schiff base as a lipid droplet-targeted fluorescent probe using Si-O-Si as a bridge for the detection of Cr6+ applied in bio-imaging

Lipid droplets are known to play an important role in many cellular activities, as revealed by recent studies. Additionally, hexavalent chromium is considered extremely toxic because it readily passes through cellular membranes and easily accumulates in living cells. In this study, a novel lipid droplet-targeted fluorescent probe (Si-LDS) for recognition of Cr6+ in living cells was designed and synthesized using triphenylamine derivatives and organosiloxane. Si-LDS detected Cr6+ with high selectivity and sensitivity. The novel probe was successfully applied to cell imaging of exogenous Cr6+ in HeLa cells, and Si-LDS was able to localize mainly in the lipid droplets of HeLa cells. Si-LDS is the first lipid droplet-targeted fluorescent probe for monitoring Cr6+.

Characterizations and mechanisms for synthesis of chitosan-coated Na-X zeolite from fly ash and As(V) adsorption study

Solid waste fly ash with low aluminum of Yunnan Province in China was used as pristine material to prepared chitosan-coated Na-X zeolite, and the obtained composite material was employed as As(V) adsorbent. Then, the prepared materials were characterized by XRD, FT-IR, and XPS. And the results suggested that the low aluminum fly ash was successfully convert into Na-X zeolite, and the mineralization between Si-OH of the obtained Na-X zeolite and C-OH of chitosan was the dominated mechanism for coated chitosan over the surface of Na-X zeolite. From the batch experiments of As(V) removal, it has been found that the coated chitosan could significantly improve As(V) performance of Na-X zeolite. The optimal working pH for removal As(V) by chitosan-coated Na-X zeolite was attained at pH 2.1 ± 0.1, and the maximum adsorption capacity was 63.23 mg/g. And the adsorption data at different interval time was excellent fitted by pseudo-second-order kinetic model. From the analyze of XPS, the results suggested that As(V) uptake over adsorbent by the bond of As-N and As-O and the surface hydroxyl group of Al-OH and -NH₂ were involved in uptake As(V) from acid wastewater.

Probing the nature of active chromium species and promotional effects of potassium in Cr/MCM-41 catalysts for methyl mercaptan abatement

The introduction of K enables a large number of CrO₄²⁻ active species to be anchored and dispersed on the surface of Cr-based catalysts.

Enhanced Performance and Conversion Pathway for Catalytic Ozonation of Methyl Mercaptan on Single-Atom Ag Deposited Three-Dimensional Ordered Mesoporous MnO2

In this study, Ag deposited three-dimensional MnO₂ porous hollow microspheres (Ag/MnO₂ PHMSs) with high dispersion of the atom level Ag species are first prepared by a novel method of redox precipitation. Due to the highly efficient utilization of downsized Ag nanoparticles, the optimal 0.3% Ag/MnO₂ PHMSs can completely degrade 70 ppm CH₃SH within 600 s, much higher than that of MnO₂ PHMSs (79%). Additionally, the catalyst retains long-term stability and can be regenerated to its initial activity through regeneration with ethanol and HCl. The results of characterization of Ag/MnO₂ PHMSs and catalytic performance tests clearly demonstrate that the proper amount of Ag incorporation not only facilitates the chemi-adsorption but also induces more formation of vacancy oxygen (O_v) and lattice oxygen (O_L) in MnO₂ as well as Ag species as activation sites to collectively favor the catalytic ozonation of CH₃SH. Ag/MnO₂ PHMSs can efficiently transform CH₃SH into CH₃SAg/CH₃S-SCH₃ and then oxidize them into SO₄^2- and CO₂ as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy. Meanwhile, electron paramagnetic resonance and scavenger tests indicate that •OH and ¹O₂ are the primary reactive species rather than surface atomic oxygen species contributing to CH₃SH removal over Ag/MnO₂ PHMSs. This work presents an efficient catalyst of single atom Ag incorporated MnO₂ PHMSs to control air pollution.