Photocatalytic adsorption/degradation of tetracycline by S-scheme BiOI/BiOIO3 p-n heterojunction from dissociation of BiOIO3in-situ solvothermal process

The pollution of tetracycline (TC) had attracted more and more attention due to its unprecedented use and potential hazards. The S-scheme BiOI/BiOIO3 p-n heterojunction was successfully fabricated by in-situ solvothermal treatment of BiOIO3, and was used for the removal of TC from aqueous solutions. The results demonstrated that the construction of S-scheme p-n heterojunction could significantly improve the removal of TC by photocatalytic adsorption/degradation synergism. The removal rate of TC was significantly enhanced after solvothermal modification. The three main reasons for the enhanced removal efficiency were as follows: first, the light absorption range of the BiOIO3 was enhanced by solvothermal treatment; secondly, the construction of the heterojunction was beneficial to the valid separation and migration of the photo-generated carriers; finally, the adsorption of TC enhanced the speed of TC reaching the semiconductor interface and reacting with active species. Trapping tests were conducted to reveal that •O2- and 1O2 are the main reactive species for TC degradation. The nine degradation products were identified by the high performance liquid chromatography-mass spectrometry (HPLC-MS), and the three reaction pathways were deduced. A possible S-scheme p-n heterojunction photocatalytic mechanism was presented on the basis of band structures and active species capturing experiment.

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)-Cr(VI)-Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

Improvement of the reduction of condensable particulate matter in flue gas scrubbing process

Condensable particulate matter (CPM) is characterized by complex composition, non-negligible emission concentration, and fine or ultrafine in size after conversion to particles, which is difficult to remove. Current methods to control CPM are not fully developed and mainly focus on synergistic removal of CPM in existing air pollution control devices, such as CPM reduction through scrubbing processes in wet flue gas desulfurization (WFGD) systems. In this work, an experimental system including a simulated WFGD scrubber, also referred to as the primary scrubber (PS), and a secondary scrubber (SS) was built to explore measures to improve the CPM reduction performance during scrubbing. The operating parameters of the liquid-to-gas (L/G) ratio and the spray temperature in the two scrubbers were tuned in the experiments. The results indicated that CPM could be reduced in the PS by conversion to filterable particulate matter (FPM), and captured by the spray droplets through the effects of dissolution and condensation, but the reduction was not very efficient. In the SS, the reduction performance of CPM could be further improved due to increased dissolution of CPM caused by increased opportunities for gas-liquid contact, and increased condensation of CPM due to lower spray temperature. The FPM transformed from the CPM in the PS could also be reduced in the SS by the effects of diffusiophoresis and thermophoresis contributed by water vapor condensation. An increase in the L/G ratio could improve the CPM reduction.

Synergistic removal of Cd(II)-organic complexes by combined permanent magnetic resins

Due to the enormous threat of pollution by heavy metal ions and organics, the effective removal of HMIs-organic complexes from various wastewater is of vital importance. In this study, synergistic removal of Cd(II) and para-aminobenzoic acid (PABA) by combined permanent magnetic anion-/cation-exchange resin (MAER/MCER) was examined in batch adsorption experiments. The Cd(II) adsorption isotherms fitted the Langmuir model at all tested conditions, suggesting a monolayer adsorption nature in both the sole and binary systems. Moreover, the Elovich kinetic model fitting demonstrated a heterogeneous diffusion of Cd(II) by the combined resins. At the organic acids (OAs) concentration of 10 mmol/L (molar ratio of OAs: Cd = 20:1), the adsorption capacities of Cd(II) by MCER decreased by 26.0, 25.2, 44.6, and 28.6%, respectively, under the coexistence of tannic acid, gallic acid, citric acid and tartaric acid, indicating the high affinity of MCER towards Cd(II). The MCER displayed high selectivity towards Cd(II) in the presence of 100 mmol/L of NaCl, with the adsorption capacity of Cd(II) decreasing by 21.4%. The "salting out" effect also promoted the uptake of PABA. Decomplexing-adsorption of Cd(II) by MCER and selective adsorption of PABA by MAER were proposed as the predominant mechanism for the synergistic removal of Cd(II) and PABA from the mixed Cd/PABA solution. The PABA bridging on MAER surface could promote the uptake of Cd(II). The combined MAER/MCER showed excellent reusability during five reuse cycles, indicative of the great potential in the removal of HMIs-organics from various wastewater.

Promotion effect of Ni doping on the oxygen resistance property of Fe/CeO2 catalyst for CO-SCR reaction: Activity test and mechanism investigation

Catalytic reduction of NO using CO, which is usually present in the flue gas of the iron and steel industry, is considered as an economical and eco-friendly de-NO_x method (CO-SCR). However, the oxygen present in the flue gas will significantly inhibit the CO-SCR activity of the catalyst, thereby limiting its industrial application. Herein, catalysts based on iron and cerium oxides were prepared and modified with different metals to investigate their performance for the CO-SCR reaction in the presence of oxygen. The results show that the Fe/CeO₂ catalyst can reach 99% NO conversion at 200 °C, but its activity decreased dramatically to 42.7% when the oxygen is present (0.5 vol%). By contrast, the NO conversion of Ni-doped Fe/CeO₂ catalyst demonstrated significant enhanced oxygen resistance and could achieve 92% even at 150 °C in the presence of 0.5 vol% oxygen. Characterization techniques such as N₂ adsorption, XRD, SEM/TEM, XPS, H₂-TPR, and in situ DRIFT were employed to investigate the mechanism of the improved oxygen resistance property of Ni-doped catalyst. The results show that the doped Ni can interact with Fe species, increases the BET surface area of the catalyst and generates more surface oxygen vacancies (SOV) and surface synergetic oxygen vacancy (SSOV) in CO-SCR reaction, thereby improving the redox performance of the catalyst. In situ DRIFT results show that the better redox performance of NiFe/CeO₂ catalyst is conducive to the conversion of adsorbed NO_x species to the reactive intermediate NO₂^- species during the reaction. Meanwhile, the enhanced SOV/SSOV in the NiFe/CeO₂ catalyst can remain active in the presence of oxygen. Therefore, the NiFe/CeO₂ catalyst exhibits a promising catalytic activity in CO-SCR reaction when oxygen is present.

A highly efficient technique to simultaneously remove acidic and basic dyes using magnetic ion-exchange microbeads

The purpose of this study was to examine the combination of magnetic anion-exchange microbeads (MAM) and magnetic cation-exchange microbeads (MCM) to remove crystal violet (CV; a basic dye) and acid green 9 (AG9; an acidic dye) from their individual and combined solutions. Adsorption kinetics and isotherms experiments were performed in batch mode. CV and AG9 displayed superior affinity towards MCM and MAM, respectively, and their combined solution was efficiently adsorbed by combining MCM and MAM. The pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models well described the adsorption kinetic data, and the pseudo-second-order model appeared a better fit for the two-component CV/AG9 system. The better fit of the Langmuir isotherm for CV adsorption indicated that CV adsorption occurred on active sites with equal affinity in the monolayer. In contrast, AG9 adsorption onto the heterogeneous MAM surface appeared to be multilayered adsorption. The adsorption capacities of the two dyes decreased with the increase in the co-existing salt concentration and increased only slightly at the high salt level due to the salting-out effect. Moreover, these microbeads maintained most of their initial capacity during five reuse cycles, indicating the great potential of MCM and MAM to remove basic and acidic dyes in practical applications.

Synergistic removal of As(V) from aqueous solution by nanozero valent iron loaded with zeolite 5A synthesized from fly ash

Nanozero valent iron (NZVI) loaded on zeolite 5A can efficiently remove As(V) in water through the synergism of zeolite 5A and NZVI. In this study, zeolite 5A was first obtained by ion exchange using zeolite 4A synthesized from fly ash and CaCl₂, and then NZVI-5A zeolite was synthesized by a reduction method to load NZVI on zeolite 5 A. NZVI-5A zeolite had a specific surface area of 238 m²/g. The As(V) removal capacity by NZVI-5A zeolite was 72.09 mg/g by the Langmuir model fitting, and the removal capacity was almost not affected by solution pH in the pH range of 4-12. As(V) was removed by the precipitation of Ca²⁺ in zeolite 5A with As(V), Ca²⁺ and NZVI with As(V), and the reduction and inner ball complex reaction of NZVI. The As(V) removal efficiency by NZVI-5A zeolite was almost unaffected by the coexistence of CO₃^2-, SO₄^2-, NO^3- and Cl^- but decreased with high concentrations of PO₄^3- in solution. The NZVI-5A zeolite could efficiently remove metal ions coexisting with As(V) in solution. The As(V) removal efficiency by the NZVI-5A zeolite was 84.0% after 5 cycles, and the NZVI-5A zeolite could be separated from the solution with an external magnetic field.

Quinones contained in wastewater as redox mediators for the synergistic removal of azo dye in microbial fuel cells

The present paper aimed to investigate the roles of quinones contained in wastewater and the enhanced effects on microbial fuel cells (MFCs) under different redox conditions. The feasibility of using wastewater rich in quinones to act as co-substrate and redox mediators (RMs) library to strengthen the synergistic removal of azo dye in MFCs was evaluated. The results demonstrated that quinones achieved enhanced effects on electricity generation and COD removal of MFC better at higher current intensity. The addition of pure quinone decreased electron transfer resistance (Rct) of MFCs from 4.76 Ω to 2.13 Ω under 1000 Ω resistance and 1.16 Ω-0.75 Ω under 50 Ω resistance. Meanwhile, higher coulombic efficiency was achieved. Compared with sodium acetate, using quinone-rich traditional Chinese medicine (TCM) wastewater as the co-substrate enhanced the synergistic removal of reactive red 2 (RR2) in MFCs from 79.58% to 92.45% during 24 h. RR2 was also degraded more thoroughly due to the accelerated electron transfer process mediated by RMs. Microbial community analysis demonstrated that the presence of quinone in TCM wastewater can enrich different exoelectrogens under varied redox conditions and thus influenced the enhanced effects on MFC. Metagenomic functional prediction results further indicated that the abundance of functional genes involved in carbohydrate metabolism, membrane transport metabolism, biofilm formation, and stress tolerance increased significantly in presence of RMs. Redundancy analyses revealed that RMs addition was the more important factor driving the variation of the microorganism community. This study revealed the potential effect of quinones as redox mediators on the bioelectrochemical system for pollutants removal.

Synergistic removal of particles, SO2, and NO2 in desulfurized flue gas during condensation

The synergistic removal of multi-pollutants, including particles, SO₂, and NO₂, is a key concern in the process of flue gas purification, during which the supersaturated environment is an essential premise for the nucleation and deep reduction of particles. The condensation of desulfurized flue gas using heat exchangers can not only recover condensed water and latent heat but also create supersaturated environment to promote the flue gas purification. In this study, an experimental system for desulfurized flue gas condensation is established. The effect and associated mechanism of condensation process on the removal of multi-pollutions are clarified. The results show that particles with an aerodynamic diameter larger than 2.5 μm accounts for 50% in mass proportion. The flue gas temperature drop has positive influence to the increase of the ideal supersaturation degree, which is beneficial for the removal of particles (especially when the aerodynamic diameter is less than 1 μm), SO₂, and NO₂. The ideal supersaturation degree slightly reduces with the rise of inlet flue gas temperature, which can promote the removal efficiency of small particles, while weaken that of large particles, SO₂, and NO₂. Caused by the increase of flue gas flow rate, the nucleation process weakens, reducing the removal efficiency of all pollutants (particles, 45.2-28.3%; SO₂, 27.5-14.5%; NO₂, 21.5-15%). On the whole, the increase of the ideal supersaturation degree contributes to the synergistic removal of pollutants especially particles with smaller radius in the flue gas. The reduction of particles with aerodynamic diameter less than 1 μm is conductive to the synergistic removal of SO₂ and NO₂.

Mechanistic insights into the enhanced removal of roxsarsone and its metabolites by a sludge-based, biochar supported zerovalent iron nanocomposite: Adsorption and redox transformation

Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant.

Synergistic removal of copper and tetracycline from aqueous solution by steam-activated bamboo-derived biochar

Steam-activated biochar (SBC) was prepared and showed excellent performance for synergistic removal of Cu²⁺ and tetracycline (TC). The adsorption capacity of SBC and mutual effect of TC and Cu²⁺ were investigated via single and binary system and the adsorption isotherm. The adsorption capacity of TC was significantly enhanced when it coexisted with Cu²⁺. Likewise, increased amounts of Cu²⁺ were adsorbed in the presence of TC. The presence of NaCl exerted a negative influence on the adsorption of Cu²⁺, while the inhibitory effect of salinity on TC was neutralized by bridge enhancement in the binary system. Bridge enhancement and site competition were involved in the synergistic removal of TC and Cu²⁺. Considering the stable application in simulated and real water samples, SBC showed great potential for synergistic removal of antibiotics and heavy metals.

Field test of SO3 removal in ultra-low emission coal-fired power plants

Under the extensive implementation of ultra-low emission (ULE) facilities in coal-fired power plants of China, sulfur trioxide (SO₃) has received increasing attention due to its impact on human health and operation safety of power plants. However, systematic research and evaluation for controlling SO₃ emission in various ULE facilities are still lacking. Here, a systematic study was conducted based on 378 in situ performance evaluation tests carried out in 148 coal-fired power plants. The results illustrate that the SO₂/SO₃ conversion rate of the selective catalytic reduction devices can be controlled within 1% before and after ULE retrofit. Also, the synergistic removal efficiency of SO₃ in the low-low-temperature electrostatic precipitator and the wet electrostatic precipitator can be higher than 70%. The removal efficiency of SO₃ in the wet limestone-gypsum flue gas desulfurization scrubber is 33-64% before ULE and 31-81% after, and the average efficiency of the double scrubbers is 8.7% higher than that of the single scrubber. Due to the different SO₃ removing abilities of various technologies, the overall efficiency of SO₃ removal is in the range between 27 and 95% adopting different ULE technical routes. Average concentration of SO₃ emission can be decreased by 51.8% after ULE application.

Synergistic removal of tylosin/sulfamethoxazole and copper by nano-hydroxyapatite modified biochar

Antibiotics and heavy metals are frequently detected simultaneously in aquatic environment. In this study, we investigated the removal performance of biochar modified with nano-hydroxyapatite (nHAP, nHAP@biochar) on tylosin (TYL) /sulfamethoxazole (SMX) and Cu(II) simultaneously. Six nHAP@biochars were prepared with different feedstock and nHAP and biomass ratios. The influences of feedstock and nHAP and biomass ratios, interaction of TYL/SMX and Cu(II) and thermodynamic study were investigated. The adsorption quantities on nHAP@biochars prepared by wood-processing residues were higher than by Chinese medicine residues. The adsorption amounts of TYL decreased with the addition of Cu(II), while the adsorption quantities of SMX increased. The adsorptions of Cu(II) were promoted by TYL and changed slightly with the increasing of SMX. Specific surface area and pore size were two of the main factors influencing the adsorption capacities of nHAP@biochars. According to density functional theory, nHAP@biochar-TYL-Cu and nHAP@biochar-Cu-SMX were more existed in the systems.

Mechanistic insights into adsorption and reduction of hexavalent chromium from water using magnetic biochar composite: Key roles of Fe3O4 and persistent free radicals

Magnetic biochar (MBC) has been used to remove hexavalent chromium (Cr(VI)) from water, but the roles of Fe₃O₄ and persistent free radicals (PFRs) in MBC in Cr(VI) removal are still less investigated. In this work, the MBC synthesized by microwave co-pyrolysis of solid-state FeSO₄ and rice husk was employed to remove Cr(VI) from water. In comparison to the rice husk biochar (BC), the MBC exhibits the 3.2- and 11.7-fold higher adsorption and reduction efficiency of Cr(VI), resulting in the higher Cr(VI) removal efficiency (84.3%) and equilibrium adsorption capacity of MBC (8.35 mg g^-1) than that (26.5% and 2.63 mg g^-1) of BC. Multiple characterization results revealed that the high Cr(VI) removal performance of MBC was mainly attributed to the presence of active Fe₃O₄ and carbon-centered PFRs in the porous and graphitic MBC. The Fe₃O₄ not only provided active chemisorption/reduction sites for Cr(VI) via its Fe(II)_oct and Fe(III)_oct coordination, but also facilitated the generation of more active electron donating carbon-centered PFRs than carbon-centered PFRs with an oxygen atom in the graphitic structure to reduce Cr(VI). The presence of Fe₃O₄ also elevated 36.7 m² g^-1 of BET-surface area and 0.043 cm² g^-1 of pore volume of MBC, promoting the Cr(VI) removal. The Fe₃O₄ and carbon-centered PFRs contributed to ∼81.8% and ∼18.2% of total Cr(III) generation, respectively. In addition, the initial solution pH was responsible for determining the relative significance of Cr(VI) adsorption and reduction. This study provides new insights into the mechanisms of Cr(VI) removal from water by the MBC.

Ternary cross-coupled nanohybrid for high-efficiency 1H-benzo[d]imidazole chemisorption

1H-Benzo[d]imidazole (BMA) has been considered as an emerging pharmaceutical organic contaminant, leading to the increasing BMA detection in wastewaters and need to be removed from ecosystem. This study investigated a highly synergistic BMA chemisorption using a novel ternary cross-coupled nanohybrid [γ-APTES]-Fe₃O₄@PAN@rGO. Magnetic nanoparticles (Fe₃O₄) were in situ core-shell co-precipitated with polyacrylonitrile polymer (PAN). Then, the prepared Fe₃O₄@PAN was decorated on hexagonal arrays of reduced graphene oxide (rGO) inside the framework of γ-aminopropyltriethoxysilane ([γ-APTES]). The final nanohybrid [γ-APTES]-Fe₃O₄@PAN@rGO produced adjacent inter-fringe distances of 0.2-0.4 nm corresponded well to (111), (220), and (311) parallel sub-lattices with two oblique intersections at 90° right angle and 60° triangle. The BMA adsorption was favorable in neutral pH 7, aroused temperature (50 °C), and controlled by endothermic process. The identified maximum adsorption capacity of 221.73 mg g^-1 was 30% higher than the reported adsorbents. The adsorption mechanisms include ion exchange, hydrogen bond, dipole-dipole force, π-conjugation, electrostatic, and hydrophobic interaction. Graphical abstract The synthetic route of novel nanohybrid [γ-APTES]-Fe₃O₄@PAN@rGO was investigated. After BMA adsorption, the adsorbent surface was entirely changed, thus an efficiently facile magnetic separation within 8s. [γ-APTES]-Fe₃O₄@PAN@rGO formed different oblique intersections of 60° and 90° sub-lattices.

Multifold enhanced synergistic removal of nickel and phosphate by a (N,Fe)-dual-functional bio-sorbent: Mechanism and application

A novel (N,Fe)-dual-functional biosorbent (N/Fe-DB) capable of efficient synergistic removal of Ni(II) and H₂PO₄^- from aqueous solution was synthesized. The adsorption capacities of Ni(II) and H₂PO₄^- were both remarkably enhanced over 3 times compared with those in single systems. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed that complexation of amino groups and ligand exchange of hydrous ferric oxide in N/Fe-DB played dominant roles. The electric double layer compressing and chelating ligand of deprotonated H₂PO₄^- accounted for the enhanced removal of Ni(II) in binary system, while cation bridge interaction promoted uptake of H₂PO₄^-. Furthermore, the coadsorbates were sequentially recovered, with the ratios of more than 99.0%. Besides, the recovered N/Fe-DB remained stable and applicable to the treatment of real electroplating wastewater even after six adsorption-regeneration cycles. Since the electroplating industry is springing up, effective control of heavy metals and phosphate has attracted global concerns. Based on the enhanced coremoval properties and superb regenerability, N/Fe-DB is potentially applicable to practical production.