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Abstract Activated carbon-coated α-Fe 2 O 3 nanoparticles (nFe 2 O 3 @AC) were synthesized by a facile impregnation method to enhance hexavalent chromium (Cr(VI)) removal from water. The SEM images confirmed that α-Fe 2 O 3 particles ranging from 90 to 500 nm were dispersedly loaded on the AC, which successfully amended Cr(VI) removal. The nFe 2 O 3 @AC was able to remove Cr(VI) with a 3 times higher efficiency of 94% in comparison with the AC. After adsorption, Cr(VI) reduction coupled with AC oxidation and low soluble (Cr x Fe 1-x)(OH) 3 precipitates were eventually formed. The Cr(VI) removal process was pH-dependent and could be well fitted to pseudo second-order kinetics. The nFe 2 O 3 @AC could be easily regenerated by 0.1 M HCl and showed a good stability as an 80% Cr(VI) removal efficiency was recorded after 4 desorption-adsorption cycles. In addition, this composite had a promising potential for repeated utilization because the AC of the adsorbed nFe 2 O 3 @AC could be refreshed and remodified with nFe 2 O 3 after stripping all the nFe 2 O 3 and (Cr x Fe 1-x)(OH) 3 precipitates from its surface by 1 M HCl and a Cr(VI) removal efficiency of 86% could be achieved. Our results demonstrated that the use of nFe 2 O 3 is an efficient and promising method to modify AC and enhance Cr(VI) removal form aqueous solutions. Graphical abstract Image 1 Highlights • Nano-sized α-Fe 2 O 3 was homogeneously distributed on activated carbon. • Cr(VI) was removed via adsorption, reduction and co-precipitation mechanism. • The nFe 2 O 3 @AC composite has good stability and reusability. [ABSTRACT FROM AUTHOR]

Pure zero-valent iron (ZVI) has poor catalytic capacity due to its agglomeration and slow corrosion rate in neutral solution and hence requires acid condition for heterogeneous Fenton reaction. In this study, we develop an activated carbon (AC)-supported ZVI catalyst (AC-Fe0) that was prepared with a one-step reductive roasting method by employing AC as a reductant and supporting matrix. The constructed ACFe 0 was then used for Fenton degradation of an azo dye reactive brilliant orange (X-GN). Analyses from multiple characterization techniques (e.g., scanning electron microscopy, X-ray diffraction, and Brunnaer-Emmett-Teller) show that ZVI particles with a diameter of about 5 lm were dispersed on the surface and pores of the AC. We show that the AC-Fe0 could be used as a highly effective catalyst for Fenton degradation of X-GN. A nearly unity efficiency of X-GN decoloration was achieved within 80 min reaction time under neutral solution condition that was attributed to the well-dispersion of ZVI particles on the AC and the formation of numerous galvanic cells between the ZVI and the AC. The decoloration of X-GN was found to follow the pseudo-first order kinetics and the apparent rate constant was measured to be 6.5 ? 10-2 min-1 at 308C. We conclude that this newly-developed AC-Fe0 technique greatly reduces the generation of massive iron-containing sludge as the remaining ferric ion in the solution was minimized (<1 mg L21) after the reaction. [ABSTRACT FROM AUTHOR]

Activated carbon-supported goethite (α-FeOOH@AC) was prepared by a simple impregnation method to catalyze hydrogen peroxide (H 2 O 2) for effective inactivation of Escherichia coli (E. coli) with α-FeOOH and AC as controls. As expected, α-FeOOH particles were uniformly distributed on AC surfaces and surface-bound Fe(III) was partially converted to Fe(II) by structural hydroxyl groups of AC. The resultant Fe(II) catalyzed H 2 O 2 to generate hydroxyl radicals (·OH) for effective E. coli inactivation by destroying its membrane and intracellular substances. The α-FeOOH@AC-H 2 O 2 system therefore achieved an effective inactivation efficiency of 4.5 log, which was much higher than 1.6 log of the α-FeOOH-H 2 O 2 system and 1.9 log of the AC-H 2 O 2 system. Besides, due to the cycle of Fe(III)/Fe(II) redox on AC surface during reaction, high inactivation efficiency and low leaching iron concentration of 0.29 mg/L could be achieved at neutral condition. In addition, the α-FeOOH@AC showed excellent stability and reusability, and the used α-FeOOH@AC could be refreshed by eluting surface-bound iron oxides and reloading α-FeOOH particles with the above impregnation method. Our study demonstrated that α-FeOOH@AC is an effective and stable heterogeneous Fenton catalyst for the inactivation of E. coli in surface water treatment. [Display omitted] • Micro-sized α-FeOOH was homogeneously loaded on activated carbon. • The α-FeOOH@AC triggered Fenton reaction for effective inactivation of E. coli. • The α-FeOOH@AC showed high stability and reusability. [ABSTRACT FROM AUTHOR]

In this study, nano-sized silver oxides were loaded on activated carbon (nAg 2 O/AC) through a facile impregnation-calcination method for enhanced bacterial inactivation from drinking water, in which Escherichia coli (E. coli) was used as target bacteria. XRD and SEM characterization confirmed that nano-sized Ag 2 O particles (50–200 nm) were successfully prepared and uniformly distributed on the surfaces and pores of AC. Due to the structural reducing groups of AC, surface-bound Ag(I) was partially converted to Ag in the nAg 2 O matrix and the resulted Ag could sterilize E. coli directly. More importantly, surface-bound Ag could catalyze O 2 and H 2 O to generate reactive oxygen species (ROS) for oxidation sterilization, thus significantly enhanced the inactivation efficiency from 0.8 log 10 CFU/mL (nAg 2 O control) and 0.2 log 10 CFU/mL (AC control) to 6.0 log 10 CFU/mL in the nAg 2 O/AC system. The inactivation process was highly pH-dependent, and neutral pH was favorable for sterilization. A sterilization efficiency of 5.2 log 10 CFU/mL could still be achieved after 5 running cycles, indicating stable sterilization performance of nAg 2 O/AC. In addition, the nAg 2 O/AC also exhibited excellent renewability since a sterilization efficiency of 5.8 log 10 CFU/mL was obtained after nAg 2 O being stripped and reloaded on the AC. These results demonstrated that nAg 2 O-modified AC is an efficient material for sterilization in water treatment. • Nano-sized Ag 2 O was homogeneously loaded on activated carbon (nAg 2 O/AC) through a facile impregnation-calcination method. • The nAg 2 O/AC activated O 2 to produce O.• 2 - radicals for enhanced inactivation of E. coli. • The nAg 2 O/AC composite showed high stability and reusability. [ABSTRACT FROM AUTHOR]

A weak electric field (WEF, 2 mA cm−2) was employed to promote Fe(III)/Fe(II) cycle on goethite-impregnated activated carbon (FeOOH@AC) filled in a continuous-flow column for enhanced Cr(VI) elimination from water. Surficial analysis and Cr species distribution showed that α-FeOOH of 0.2–1 μm was successfully synthesized and evenly loaded onto AC. Electron transfer from WEF to α-FeOOH was facilitated with AC as electron shuttles, thereby boosting Fe(III) reduction in the α-FeOOH. The generated Fe(II) reduced Cr(VI) and the resultant Cr(III) subsequently precipitated with OH− and Fe(III) to form Cr(OH) 3 and (Cr χ Fe 1-χ)(OH) 3. Therefore, the WEF-FeOOH@AC column exhibited a much lower Cr(VI) migration rate of 0.0018 cm PV−1 in comparison with 0.0037 cm PV−1 of the FeOOH@AC column, equal to 104 % higher Cr(VI) elimination capacity and 90 % longer column service life-span. Additionally, under different Cr(VI) loadings by varying either seepage velocities or influent Cr(VI) concentrations, the WEF-FeOOH@AC column maintained 1.0–1.5 folds higher Cr(VI) elimination and 0.9–1.4 folds longer longevity than those of the FeOOH@AC column owing to the interaction between FeOOH@AC and WEF. Our research demonstrated that WEF-FeOOH@AC was a potential method to promote Cr(VI) elimination from water and offer an effective strategy to facilitate Fe(III)/Fe(II) cycle in iron oxides. [Display omitted] • Weak electric field promoted Fe(III)/Fe(II) cycle on FeOOH@AC by transferring cathodic electrons with AC as shuttles. • WEF-FeOOH@AC could effectively eliminate Cr(VI) by adsorption, reduction, and sequestration. • The WEF-FeOOH@AC column also exhibited excellent resistance to shock Cr(VI) loadings. [ABSTRACT FROM AUTHOR]

In this study, nano α-FeOOH (nFeOOH, 100–500 nm) was coated onto activated carbon (nFeOOH@AC) through a dipping means for enhanced Cr(VI) immobilization from drinking water. The nFeOOH@AC significantly improved the Cr(VI) removal from 19.9% (AC control) to 93.4%. XPS spectra and chromium speciation demonstrated that about 90% of adsorbed Cr(VI) was converted to Cr(III) by the nFeOOH@AC, accompanying with a reduction-oxidation of Fe3+/Fe2+ in the nFeOOH matrix due to electrons delivering between AC and surface-bound Cr(VI). The resultant Cr(III) subsequently reacted with Fe(III) to generate stable (Cr χ Fe 1-χ)(OH) 3 precipitates, leading to a much lower Cr(III) release of 7.5% back to solution by the nFeOOH@AC as compared to the AC control of 33.8%, indicating that the nFeOOH@AC had a prospective potential for Cr(VI) immobilization and decreased Cr residue in treated drinking water. Results from column experiment also showed that the nFeOOH@AC afforded a 3.5 times higher capacity for Cr(VI) immobilization and a 3.4 times longer life-span than the pristine AC. Besides, Cr(VI) immobilization by the nFeOOH@AC was a pH-dependent process and the adsorbed Cr on the nFeOOH@AC could be readily desorbed with acetic acid. The disabled nFeOOH@AC could be refreshed by recoating nFeOOH particles with the above dipping method after stripping all the iron oxides with hydrochloric acid. This study demonstrated that nFeOOH coating is an efficient approach to enhance Cr(VI) elimination by AC during drinking water treatments. Image 1 • Nano-FeOOH coating significantly improved Cr(VI) removal and reduced Cr residue by activated carbon (AC). • Remarkable Cr(VI) immobilization and longer life-span were achieved in nFeOOH@AC column. • Cr(VI) was eliminated via adsorption, reduction and coprecipitation in nFeOOH matrix. [ABSTRACT FROM AUTHOR]

Abstract In this study, activated carbon (AC) was modified with micro-sized geothite (mFeOOH) using a facile and cost-effective impregnation method for enhanced Cr(VI) removal from aqueous solutions. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis showed that FeOOH particles with a diameter of 0.1–1 μm were dispersed homogeneously on the surfaces and pores of the AC. Fourier transform infrared spectrum (FTIR) and X-ray photoelectron spectra (XPS) analysis indicated that Cr(VI) was easily adsorbed onto the mFeOOH and reduced to Cr(III) by the AC, eventually deposited as Cr(III)-Fe(III) hydroxides (e.g., (Cr x Fe 1−x)(OH) 3). Hence, the mFeOOH@AC achieved a significantly higher Cr(VI) removal efficiency of 90.4%, 4.5 times of that the AC. The adsorption of Cr(VI) onto the mFeOOH@AC agreed well with the Langmuir adsorption model, demonstrating that the adsorption process was controlled by monolayer adsorption. This adsorption process also followed the pseudo second-order kinetics and the adsorption rate constant K 2 was determined to be 0.013 g/mg·min. The Cr(VI) removal efficiency decreased with pH values as the adsorption process was highly pH-dependent. After the desorption-adsorption process by 0.1 M HCl solution for 4 cycles, the removal efficiency of Cr(VI) was still kept up to 75.1%, indicating that the mFeOOH@AC has a good stability and can be easily regenerated. In addition, the mFeOOH@AC also exhibited a promising potential for reutilization since a Cr(VI) removal efficiency of 85.4% was achieved after stripping all the mFeOOH and Cr(III)-Fe(III) hydroxides by 1 M HCl solution and regeneration with mFeOOH. We demonstrate that the modified AC with micro-sized goethite can remarkably enhance its ability for Cr(VI) removal in water treatment. Graphical abstract Unlabelled Image Highlights • Micro-sized FeOOH was homogeneously distributed on activated carbon. • Cr(VI) was removed via adsorption, reduction and co-precipitation mechanism. • The mFeOOH@AC composite has good stability and reusability. [ABSTRACT FROM AUTHOR]

Bone char catalyzed dechlorination of trichloroethylene (TCE) by green rust (iron(II)-iron(III) hydroxide, GR) has introduced a promising new reaction platform for degradation of chlorinated solvents. This study aimed to reveal whether a broader class of biochars are catalytically active for the dechlorination reaction and to identify which biochar properties are the most important for the catalytic activity. Biochars produced by pyrolysis of animal, plant, and sewage waste substrates at 950 °C were prepared for catalytic dechlorination of TCE by GR tested in batch experiments with 0.15 g L−1 biochar, 3.2 g L−1 GR, and ~ 20 µM TCE. The results showed that the biochar substrate significantly affects its catalytic activity, with the highest TCE reduction rate observed for bone and shrimp-based biochars (k ≥ 0.18 h−1), whereas no reactivity was seen for graphite and activated carbon references. Multivariate regression indicated that the biochar catalytic activity is controlled by multiple biochar properties - biochar surface area, TCE sorption, abundance of C–O groups, and pore size are the properties that impact the catalytic activity most. Derivation of biochar reactivity relationship for a broad spectrum of biochars provides a new approach for identifying proper biochar catalysts for pollutant degradation. ga1 • Biochar reactivity for catalyzing dechlorination of trichloroethylene (TCE) varies. • The extent of TCE conversion to acetylene is biochar dependent. • Graphite and activated carbon have no catalytic activity. • Graphitic structure and O functional groups are critical. • High surface area and high TCE adsorption to biochar stimulate biochar reactivity. [ABSTRACT FROM AUTHOR]