One-step synthesis of silicon carbide foams supported hierarchical porous sludge-derived activated carbon as efficient odor gas adsorbent

Self-Accelerating Interfacial Catalytic Elimination of Gaseous Sulfur-Containing Volatile Organic Compounds as Microbubbles in a Facet-Engineered Three-Dimensional BiOCl Sponge Fenton-Like Process

The elimination of gaseous sulfur-containing volatile organic compounds (S-VOCs) by a microbubble-assisted Fenton-like process is an innovative strategy. Herein, we established a microbubble-assisted Fenton-like process to eliminate malodorous microbubble CH₃SH as representative gaseous S-VOCs, in which BiOCl nanosheets loaded on a three-dimensional sponge were exposed to (001) or (010) facets and induced Fenton-like interface reactions. Intriguingly, the microbubble-assisted Fenton-like process significantly removed 99.9% of CH₃SH, higher than that of the macrobubble-assisted Fenton-like process (39.0%). The self-accelerating interfacial catalytic mechanism was in-depth identified by in situ ATR-FTIR, PTR-TOF-MS, EPR, and DFT computational study. The extraordinary elimination performance of microbubble-assisted Fenton-like process lies in the enhancing dissolution/mass transfer of gaseous CH₃SH in the gas/liquid phase and the tight contact between CH₃SH-microbubbles and 3D-BiOCl sponge due to the low rising velocity (0.13 mm s^-1) and negative charge (-45.53 mV) of CH₃SH-microbubbles, as well as the effective generation of ¹O₂ by activating the enriched dissolved oxygen in CH₃SH-microbubble via effective electron-polarized sites on 3D-BiOCl sponge. Furthermore, CH₃SH-microbubbles transferred electrons to H₂O₂ through electron-rich oxygen vacancy centers of the 3D-BiOCl sponge to generate more •OH, thus achieving excellent elimination performance. Overall, this study demonstrates the enhanced self-accelerating interfacial catalytic elimination by S-VOC microbubble and provides the underlying mechanisms.

Dual role of O2 concentration on the reducing gases produced and NO reduction during sewage sludge combustion in pilot scale cement precalciner

The reducing gases produced and NO reduction by sewage sludge combustion were investigated in a self-made cement precalciner. The dual role of O₂ concentration (0-5 vol%) in the production characteristics of reducing gases and the reduction efficiency of NO were evaluated experimentally. TG-FTIR analysis demonstrated that the key reducing gaseous species produced by sewage sludge combustion were HCN, NH₃, CO, and CH₄. And experiments demonstrated that O₂ concentration had pronounced effects on NH₃ distribution, the maximum production rate was obtained at an O₂ concentration of 3 vol%. Meanwhile, the reducing gases NH₃ and CO were the key species for NO reduction in the cement precalciner, and the reduction efficiency of NO, when reduced by NH₃, increased with an increase in O₂ concentration, while the reduction performance of NO by CO was limited by O₂ concentration. Therefore, O₂ concentration greatly influences NO reduction efficiency by sewage sludge combustion; the maximum NO reduction efficiency was 61.67% at an O₂ concentration of 3 vol%. The difference in NO reduction by sewage sludge combustion under different O₂ concentrations was primarily attributed to NH₃ production rate and NO reduction by NH₃ and CO, which is greatly affected by O₂ concentration. Sewage sludge combustion can result in NO reduction in the cement kiln flue gas and resource utilisation of sewage sludge.

Enhanced Catalytic Ozonation for Eliminating CH3SH via Graphene-Supported Positively Charged Atomic Pt Undergoing Pt2+/Pt4+ Redox Cycle

Constructing catalysts with electronic metal-support interaction (EMSI) is promising for catalytic reactions. Herein, graphene-supported positively charged (Pt²⁺/Pt⁴⁺) atomically dispersed Pt catalysts (AD-Pt-G) with Pt_xC₃ (x = 1, 2, and 4)-based EMSI coordination structures are achieved for boosting the catalytic ozonation for odorous CH₃SH removal. A CH₃SH removal efficiency of 91.5% can be obtained during catalytic ozonation using optimum 0.5AD-Pt-G within 12 h under a gas hourly space velocity of 60,000 mL h^-1 g^-1, whereas that of pure graphene is 40.4%. Proton transfer reaction time-of-flight mass spectrometry, in situ diffuse reflectance infrared Fourier transform spectroscopy/Raman, and electron spin resonance verify that the Pt_xC₃ coordination structure with atomic Pt²⁺ sites on AD-Pt-G can activate O₂ to generate peroxide species (*O₂) for partial oxidation of CH₃SH during the adsorption period and trigger O₃ into surface atomic oxygen (*O_ad), *O₂, and superoxide radicals (·O₂^-) to accomplish a stable, high-efficiency, and deeper oxidation of CH₃SH during the catalytic ozonation stage. Moreover, the results of XPS and DFT calculation imply the occurrence of Pt²⁺ → Pt⁴⁺ → Pt²⁺ recirculation on Pt_xC₃ for AD-Pt-G to maintain the continuous catalytic ozonation for 12 h, i.e., Pt²⁺ species devote electrons in 5d-orbitals to activate O₃, while Pt⁴⁺ species can be reduced back to Pt²⁺ via capturing electrons from CH₃SH. This study can provide novel insights into the development of atomically dispersed Pt catalysts with a strong EMSI effect to realize excellent catalytic ozonation for air purification.

Preparation of binder-less activated char briquettes from pyrolysis of sewage sludge for liquid-phase adsorption of methylene blue

Binder-less activated char briquettes from sewage sludge were prepared and used for the liquid-phase adsorption of methylene blue. The properties of sludge char briquettes prepared under the different initial sludge moisture content, compression pressure, and heating rate were systematically investigated through the tests of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), surface and mechanical properties, burn-off rates, methylene blue adsorption kinetics and isotherms. All of the prepared briquettes presented hierarchical structures and microporous/mesoporous characteristics, and the increase of initial sludge moisture content from 10 to 30 wt% resulted in a great increase of surface area (S_BET), total pore volume (V_T), apparent density, and a slight decrease of mechanical performance. The decrease of compression pressure markedly enhanced the equilibrium adsorption capacity (q_{e, exp}), owing to the decreased diffusion resistance and blockage of diffusion pathways inside briquettes. In consideration of the mechanical performance and adsorption capacity, the optimum preparation condition was obtained at the initial moisture content of 30 wt%, compression pressure of 25 MPa, and heating rate of 10 °C/min, in which the axial compressive strength (ACS) and q_{e, exp} of the prepared briquettes were as high as 22.2 ± 3.1 kg/m² and 316.9 mg/g. The results also showed that the equilibrium adsorption data fit well into the pseudo-first order model system, and the adsorption isotherms followed the Langmuir isotherm model, suggesting that the adsorption process was attributed to physical adsorption, and was inclined to happen on the adsorption sites with the same energy level. Finally, the thermal regeneration tests demonstrated that the binder-less briquette had a good regeneration performance and was worthy of reusing for industrial applications.

High Removal Efficiency of Diatomite-Based X Zeolite for Cu2+ and Zn2

Diatomite-based X zeolite was obtained and its crystallinity, morphology, and interface properties were investigated by XRD, BET, SEM, EDS, and XRF. The obtained X zeolite possessed a unique meso-microporous structure and showed good ion exchange properties for Cu²⁺ and Zn²⁺. The pseudo-second-order model and Langmuir isotherm model can best describe the adsorption kinetics and isotherms of Cu²⁺ and Zn²⁺, respectively. The maximal adsorption capacities of X zeolite for Cu²⁺ and Zn²⁺ were 146 and 195 mg/g at 323 K, respectively. Meanwhile, the adsorption process for Cu²⁺ and Zn²⁺ were chemical adsorption and ion exchange, respectively. Furthermore, the adsorption data turned out to be an endothermic and spontaneous process. Compared with other reported materials, the adsorption capacity of X zeolite synthesized from diatomite was among the highest. Therefore, it could be a promising adsorbent for the disposal of wastewater that contains metal ions.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Synthesis of an easily recyclable and safe adsorbent from sludge pyrochar for ciprofloxacin adsorption

Utilization of sludge pyrochar (SP) is the terminal step to loop the entire harmless disposal process of sewage sludge with pyrolysis. A new, easily recyclable, and safe adsorbent with well-immobilized heavy metals (HMs) was prepared from SP for ciprofloxacin (CIP) adsorption. The operational conditions for the adsorbent preparation were systematically optimized based on recycling rate and adsorption performance. Additionally, the adsorption conditions, adsorption kinetics, isotherms, and regeneration of adsorbents were further investigated in the present study. The results showed that easily recyclable and safe adsorbents were successfully prepared at 1100 °C under N₂ atmospheric conditions (SPA-N-1100) with a maximum CIP adsorption capacity of 10.42 mg/g. SPA-N-1100 exhibited good CIP adsorption performance at an adsorption temperature of 45 °C and pH between 8.0 and 9.0. The adsorbents were regenerated by thermal desorption at 450 °C with a thorough decomposition of CIP. The adsorption mechanism was mainly dominated by its special porous microspheres-accumulation structure and surface species (e.g., FeP and graphite). Moreover, HMs in the adsorbents were well immobilized in SPA-N-1100 by the generation of new metal mineral phases and encapsulation of melting minerals, which had an ultralow potential for ecological risk during application.

Study on the influencing factors of removal of NOX from cement kiln flue gas by sewage sludge as a denitration agent

Experimental study on the influencing factors of using sewage sludge as a denitration agent for cement industry was carried out on a self-made laboratory-scale fluid-bed reactor. Results indicate that sludge combustion at 900 °C shows an ideal NO_X (the sum of NO and NO₂) removal activity under simulated working conditions of cement precalciner. The optimal removal efficiency of NO_X can reach 70.36 ± 3.59% in the presence of cement raw meal (CRM) at a sludge particle size range of 0.18-0.25 mm and the sludge dosage of 0.75 g/min. Besides, the NO_X removal efficiency increases to 76.94 ± 5.02% in the absence of CRM, indicating that cement raw meal inhibits the NO_X removal. This phenomenon may be attributed to the fact that CRM has promotion effect on NH₃ produced and obvious inhibitory effect on CO produced; while NH₃ and CO play a leading role in NO_X reduction, the combined effect leads to the decrease of NO_X removal. Moreover, the relationship between the composition of CRM on the inhibition of NO_X removal is MgO < CaCO₃ < CRM < Al₂O₃ <Fe₂O₃. Meanwhile, the effect of additive variety on the sludge denitration activity indicates that urea significantly promotes the NO_X removal, which is attributed to the decomposition of urea to form NH₃. The stability experiment shows that sludge denitration efficiency remains stable above 70% in the presence of CRM and can reach over 80% when adding appropriate urea. This method can realize the removal of NO_X in the cement kiln flue gas and the resource utilization of sludge. It is a promising method for sludge disposal.

From macroalgae to porous graphitized nitrogen-doped biochars - Using aquatic biota to treat polycyclic aromatic hydrocarbons-contaminated water

Enhanced macroalgal biochars with large specific surface areas (up to 399 m² g^-1), partly graphitized structure, high nitrogen doping (up to 6.14%), and hydrophobicity were fabricated by co-carbonization of macroaglae, ferric chloride, and zinc chloride. These biochars were used as sorbents for the removal of polycyclic aromatic hydrocarbons from water. The sorption capacity of polycyclic aromatic hydrocarbons onto macroalgal biochars was high (up to 90 mg g^-1), and recycling by thermal desorption was practicable. We revealed the physical-dominated multilayer sorption process, based on results from characterization and sorption experiments. Pore filling, mass transfer, π-π stacking, and the partition effect were found to be possible sorption mechanisms. This study suggests that porous graphitized nitrogen-doped biochars may be synthesized from macroalgae with simple one-pot carbonization and display promising applicability for sorption removal of organic pollutants from water.

Hydrothermal route-enabled synthesis of sludge-derived carbon with oxygen functional groups for bisphenol A degradation through activation of peroxymonosulfate

A considerable amount of sewage sludge (SS) is generated from wastewater treatment process, which is hazardous to the environment and in urge to be disposed. In this study, for the first time, we prepared carbocatalyst with abundant surface oxygen functional groups using the hazardous waste of SS as precursor via a facile hydrothermal coupled pyrolysis process. The hydrothermal treatment was found to be crucial for enhancing the oxygen content of sludge carbon (SC), most of which existed as ketonic groups. Catalytic performances of the developed SCs were examined by activating peroxymonosulfate (PMS) to degrade bisphenol A (BPA). Sample with more ketonic group performed better for BPA degradation. Under optimal reaction conditions, 100 % of BPA and 69.53 % of TOC could be removed in 20 min. Singlet oxygen (¹O₂) was suggested to be the main reactive oxygen species for degrading BPA and a BPA degradation pathway was proposed. The BPA solution showed decreased bio-toxicity after the oxidation process according to the acute ecotoxicity test. This study demonstrated the importance of surface functional groups on carbocatalyst for advanced oxidation process, which could be induced by a facile hydrothermal treatment. The feasibility of utilizing hazardous SS for advanced carbocatalyst fabrication was also revealed.

Activation of persulfate by CuO-sludge-derived carbon dispersed on silicon carbide foams for odorous methyl mercaptan elimination: identification of reactive oxygen species

In this work, sludge-derived carbon (SC) was innovatively integrated with copper oxide (CuO) on macroporous silicon carbide foams to construct a distinctive catalyst (CuO/SC) with strong catalytic activity, which can effectively activate persulfate (PS) for the removal of methyl mercaptan (CH₃SH). The structure and morphology of CuO/SC were investigated by means of XRD, SEM, and EDS. The effects of initial pH values, copper contents, PS dosages, and flow rates on CH₃SH removal were also investigated. Under optimal condition, more than 90% of CH₃SH was removed by CuO/SC-PS combined system within 10-min reaction due to the synergistic function of CuO and SC. More importantly, on the basis of reactive species trapping and ESR spectroscopy, it is revealed that the responsible reactive species for catalytic CH₃SH composition were ·SO₄^-, ·OH, ¹O₂, and ·O₂^- in CuO/SC-PS system. Finally, the possible PS activation scheme of CuO/SC samples was proposed.

Study on the degradation of accumulated bisphenol S and regeneration of magnetic sludge-derived biochar upon microwave irritation in the presence of hydrogen peroxide for application in integrated process

Based on the multi-functional magnetic sludge-derived biochar (MSBC), an innovative integrated process-coupling accumulation by adsorbing, degradation by microwave (MW)-induced catalytic oxidation in the presence of H₂O₂ and the regeneration of adsorbent simultaneously, was proposed. In this study, bisphenol S (4,4'-sulfonyldiphenol) was chosen as the pollutant model, its behaviors and related mechanism of BPS and MSBC in MW + H₂O₂ system were investigated. The BPS effective degradation on MSBC was proved by decoupling the adsorption and degradation with solvent extraction. OH and h⁺ play vital roles based on the scavenger tests. The synergistic effects of hot-spot of microwave irradiation, activation of H₂O₂, and charge transfer-induced doping effects of MSBC were attributed to the reactions. This work proves the feasibility in economics and energy-save treatment approach for low concentration organic pollutants in water.

Synthesis of CH3I-quaternized polypropylene nonwoven fiber grafted with imidazole (PP-g-Vim) to adsorb vapor phase ammonia

Ammonia in gas phase has an unpleasant smell and is hazardous to human health. Though activated carbon has been widely used as a representative adsorbent, it is significantly vulnerable to humidity. In the study, a nonwoven fibrous polypropylene polymer was synthesized using a photo-graft reaction with imidazole followed by quaternization with CH₃I. The time of each reaction was optimized for the maximum adsorption. The FT-IR confirmed that 1-vinyl imidazole (Vim) and methyl group (-CH₃) were successfully introduced into PP fibers. The Langmuir isotherm characterized that the adsorption capacity was 44.84 mg NO₃-N g^-1. The adsorption intensity, 1/n, by Freundlich adsorption isotherm was 0.41 indicating that the adsorption of NO₃-N onto PP-g-Vim-CH₃I was favorable at the studied conditions. In the gas phase, maximum adsorption of was calculated to be 40 ± 0.69 mg NH₃ g^-1 by BET model. Though the adsorption amount decreased by 2.5 times as the temperature increased from 15 °C to 45 °C, the amounts and rates of adsorption were not influenced by humidity. In conclusion, the synthesized PP-g-Vim-CH₃I was able to ammonia in the gas phase at a range of humidity.

Mechanistic study on NO reduction by sludge reburning in a pilot scale cement precalciner with different CO2 concentrations

The reducing gases of CO and NH₃ produced by sludge reburning make a major contribution to NO reduction.

Three-dimensional hierarchical porous sludge-derived carbon supported on silicon carbide foams as effective and stable Fenton-like catalyst for odorous methyl mercaptan elimination

The poor reusability of catalysts and secondary pollution are critical issues for sulfur-containing volatile organic compounds (S-VOCs) removal. In this paper, a three-dimensional (3D) hierarchical porous sludge-derived carbon supported on silicon carbide foams (SiC) has been fabricated for deep decomposition of S-VOCs under ambient conditions. The sludge-derived Fenton-like catalyst has been confirmed to be hierarchical 3D porous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Nitrogen adsorption-desorption measurements and Raman spectroscopy. Significantly, the catalyst after KOH activation (SC_FeK-SiC) shows excellent catalytic decomposition of methyl mercaptan (CH₃SH) with almost complete CH₃SH oxidation into sulfate using hydrogen peroxide as an oxidant under ambient conditions. This catalyst also possesses relative low iron dissolution and excellent cycling performance. The efficient catalytic ability of SC_FeK-SiC can be attributed to SiC foam functioned as a stable 3D macroporous skeleton, in which the porous sludge-derived carbon immobilizes the active iron species and promotes the efficient capture of gaseous CH₃SH, thus facilitating the decomposition of CH₃SH by generating reactive species, specifically ·OH. The reaction mechanism was systematically investigated. Herein, the design of the porous sludge-derived carbonaceous Fenton-like catalyst paves an avenue for efficient VOCs treatment and rational sludge disposal.