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Today, new energy sources alternative to fossil fuels are needed to meet the increasing energy demand. It is becoming increasingly important to constitute new energy sources from waste biomass through the liquefaction process. In this study, walnut shells (WS) were liquefied catalytically and non-catalytically under different parameters using the liquefaction method. In this process, the effect of silica fume/nano zero-valent iron (SF/NZVI) catalysts on the conversion rates was investigated. The catalyst was synthesized by reducing NZVI using a liquid phase chemical reduction method on SF. The SF/NZVI catalyst was characterized by scanning electron microscopy- energy dispersive X-ray (SEM–EDX), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis. The effect of various process parameters on the liquefaction process was investigated. In this context, the reaction temperature ranged from 300 to 400 °C, the solid/solvent ratio ranged from 1/1 to 1/3, the reaction time ranged from 30 to 90 min, and the catalyst concentration ranged from 1 to 6%. According to the results obtained, the most suitable operating conditions for non-catalytic experiments in liquefaction of WS were found to be temperature of 400 °C, reaction time of 60 min, and solid/solvent of 1/3. In catalytic conditions, the optimum values were obtained as temperature of 375 °C, reaction time of 60 min, solid/solvent ratio of 1/3, and catalyst concentration of 6%. The highest total conversion and (oil + gas) % conversion were 90.4% and 46.7% under non-catalytic conditions and 90.7% and 62.3% under catalytic conditions, respectively. Gas chromatography/mass spectrometry (GC/MS) analysis revealed the bio-oil was mainly composed of aromatic compounds (benzene, butyl-, indane and their derivatives,) and polyaromatic compounds (naphthalene, decahydro-, cis-, naphthalene, 1-methyl-.). The aim of increasing the quantity and quality of the light liquid product in the study has been achieved. [ABSTRACT FROM AUTHOR]

The aggregation of nanoscale zero-valent iron (NZVI) is one of the biggest challenges for its application when treating contaminants in aquatic environment. We report a study on synthesis of sodium carbonate-modified biochar (BC-600) combined with sodium alginate (SA)-modified NZVI (SA/NZVI@BC-600) for the removal of tetracycline (TC). When the initial concentration of TC was 20 mg/L, 100% TC was removed by SA/NZVI@BC-600 at an initial pH of 7 under room temperature of 25 °C within 90 min. In addition, the reactivity of the SA/NZVI@BC-600 composites toward TC removal was not obviously declined after 4 cycles. SA/NZVI@BC-600 shows high reactivity, stability, and reusability. This excellent performance of SA/NZVI@BC-600 was related to the addition of SA and BC-600. The best performance of the SA/NZVI@BC-600 system was observed under weakly acidic and neutral conditions. Increasing the initial concentration and lowering the reaction temperature had a slight negative effect on the removal of TC by SA/NZVI@BC-600. In addition, the presence of CO32− and HCO3− had a significant negative effect on the degradation of TC. Meanwhile, ·OH and ·O2− played the leading role in TC degradation. This study not only reported a novel strategy of synthesizing an excellent BC modified NZVI based catalyst but also evaluated its promising application for antibiotic degradation in aqueous solution. [ABSTRACT FROM AUTHOR]

The degradation of formaldehyde in a photo-Fenton reaction was studied using n-ZVI/TiO2 as the catalyst. The effects of %n-ZVI loading, catalyst dosage, H2O2, and pH on formaldehyde degradation were studied. The n-ZVI/TiO2 catalysts were prepared by impregnation with chemical reduction, and their catalytic activity was evaluated in a batch reactor under UVC light. Transmission electron microscopy (TEM) was used to determine that the n-ZVI nanoparticle size was 39.41 nm. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation states of 2%n‑ZVI/TiO2, and the Fe 2p spectrum of 2%n-ZVI/TiO2 indicated the presence of Fe0. The optimal conditions for the complete removal of formaldehyde within 30 min were an n-ZVI loading of 2 wt.%, a catalyst dosage of 0.5 g/L, 30 mM H2O2, and an initial pH of 3. After the reaction, the C–H functional group of formaldehyde was not observed due to the •OH radicals generated by Fe0 and H2O2 attacking the formaldehyde molecule. Moreover, no Fe leaching was observed, presenting an advantage compared with homogeneous Fe catalysts. Therefore, 2%n‑ZVI/TiO2 shows excellent potential as a photo-Fenton catalyst for the environmentally friendly degradation of formaldehyde. [ABSTRACT FROM AUTHOR]

A novel composite (nZVI/HNTs) was prepared via incorporating nano zero-valent iron (nZVI) on halloysite nanotubes (HNTs) for degrading tetracycline hydrochloride (TCH) with existence of persulfate (PS). The adsorption process of nZVI/HNTs to TCH conformed to the Freundlich isotherm model and pseudo-second-order kinetic model, and its maximum adsorption capacity was 76.62 mg·g−1. Furthermore, the nZVI/HNTs + PS system exhibited satisfactory degradation efficiency (84.21%) for TCH, and stable nZVI/HNTs (Fe leaching < 0.001 mg·L−1) could be reused. When nZVI/HNTs dosage, PS dosage and temperature increased, TCH degradation could be enhanced. After four cycling, nZVI/HNTs + PS system had still 65.8% degradation for TCH. The quenching tests and EPR analysis evidenced that SO4•− was predominant instead of •OH in such system. Three possible pathways of TCH degradation were provided through the liquid chromatograph-mass spectrometer (LC–MS) determination. Meanwhile, the biological toxicity prediction analysis indicated that the nZVI/HNTs + PS system would be an environment friendly treatment method toward TCH pollution. [ABSTRACT FROM AUTHOR]

In this study, nano zero-valent iron (nZVI) was used as the Fe2+ source in the Fenton reaction, and a UV-nZVI-H2O2 system was constructed to efficiently degrade and mineralize refractory organic matter in landfill leachate. The results showed that under the optimal conditions (initial pH = 3, UV = 14 W, nZVI = 0.5 g/L, and [H2O2] = 30 mM), the removal efficiencies of total organic carbon, absorbance at 254 nm, and color number were 61.38%, 83.89%, and 85.79%, respectively. Control experiments show that the UV-nZVI-H2O2 system has the highest removal rate and mineralization rate of refractory organic matter. The excellent performance of the UV-nZVI-H2O2 system is related to a higher H2O2 utilization rate. The H2O2 residue in the UV-nZVI-H2O2 system was the lowest, and the effective utilization rate of H2O2 was as high as 98.80%. Alcohol quenching experiments and hydroxyl radical quantitative experiments showed that the dominant reactive oxygen species in the UV-nZVI-H2O2 system was HO• and the yield of HO• was as high as 2007.80 μM, which was much higher than that in other systems. The results of spectra analysis showed that the low molecular weight, high fluorescence frequency organic matter, and relatively stable aromatic organic matter were significantly degraded after treatment with the UV-nZVI-H2O2 system and the aromatic degree, humification degree, molecular weight, and molecular polymerization degree of refractory organic matter were also significantly decreased. The mechanism of the UV-nZVI-H2O2 reaction includes homogeneous and heterogeneous Fenton reactions and adsorption and precipitation of organic matter by iron-based colloids. This study can provide theoretical and technical support for the advanced treatment of refractory organic matter in landfill leachate. [ABSTRACT FROM AUTHOR]

Given their considerable solubility in water and potentially high toxicity to human health, organoarsenic compounds have become an emerging contaminant. Herein, a heterogeneous Fenton process mediated by SiO2-coated nano zero-valent iron (SiO2-nZVI) was employed to simultaneously remove the p-arsanilic acid (p-ASA, a typical organoarsenic compound) and the released arsenic. The initial pH value significantly influenced on the degradation of p-ASA and at the optimal pH (3.0), p-ASA (10 mg L−1) could be completely oxidized to As(V), NH4+, and plentiful phenolic compounds such as phenol and p-hydroquinone via the cleavage of C–N and C–As bonds within 60 min in pure water. Meanwhile, although the formed lepidocrocite and magnetite on the surface of SiO2-nZVI significantly limited the reutilization, they played a vital role in the adsorption of the released As(V) and the residual arsenic levels in the effluent were as low as 0.031 mg L−1, meeting both the drinking water standard of the World Health Organization (WHO) and the surface water standard of China (0.05 mg L−1). Furthermore, high-level dissolved organic matters (DOM) (> 2 mg C L−1) exhibited strong interference with both the oxidation of p-ASA and adsorption of arsenic, but the interference could be eliminated by increasing the SiO2-nZVI dosage or adding H2O2. Importantly, this system could completely remediate p-ASA in a short time and simultaneously avoid the secondary pollution caused by inorganic arsenic, which was significant for the remediation of organoarsenic pollutants in swine wastewater. [ABSTRACT FROM AUTHOR]

Nano zero-valent iron (nZVI) is one of the most paramount nanoparticles (NPs) applied in environmental remediation, leading to great concerns for the potential impacts on soil ecosystem health. The objective of this study was to link toxicokinetics and consumer–resource dynamics in the Caenorhabditis elegans–Escherichia coli (worm–bacteria) ecosystem. The biokinetic parameters of bacteria and worms were obtained from toxicokinetic experiments and related published literature. Biomass dynamics of bacteria and worms were estimated by employing the modified Lotka–Volterra model. Dynamics of bacteria and worm biomass, internal concentrations of nZVI, bioconcentration factors (BCFs), and biomagnification factors (BMFs) were simulated based on the consumer–resource dynamics. Results showed that the biomass of worms steadily increased from 22.25 to 291.49 g L−1, whereas the biomass of bacteria decreased from 17.17 to 4.70 × 10−8 g L−1 after 96-h exposures of nZVI. We also observed ratios of nZVI concentrations in worms and bacteria increased from 0.06 to 26.60 after 96 h. Moreover, decrements of the bioconcentration factor of E. coli (BCFE) values from 0.82 to 0.03 after 96 h were observed, whereas values of BMFs increased from 0.06 to 57.62 after 96 h. Internal concentrations of nZVI in worms were found to be mainly influenced by the ingestion rate of bacteria by worms, and the biomass conversion of bacteria had the lowest effect. Implementation of the integrated bioaccumulation–consumer–resource model supports the hypothesis that the C. elegans–E. coli dynamics of internal nZVI concentrations could be effectively associated with the predator–prey behavior and was dominated by the same physiological parameter in the two biological systems. [ABSTRACT FROM AUTHOR]

The effects of humic acid (HA) and its different molecular weight (MW) fractions on the sedimentation of nanoscale zero-valent iron (NZVI) in the absence and presence of cations (i.e., Na+/Mg2+/Ca2+) were investigated. Ultrafiltration (UF) was used as the method of fractionation to obtain four different MW fractions (separated by ultrafiltration membranes of 10 kDa, 50 kDa, and 100 kDa). Differing sedimentation behavior was observed for NZVI with different MW fractions of HA. Generally, the degree of settling of NZVI particles in the presence of high MW fractions of HA was lower than that of low MW fractions of HA and that without HA. The results were mainly attributed to the steric stabilization provided by the high MW fractions of HA. The presence of Na+/Mg2+/Ca2+ alone had insignificant influence on the settling of NZVI, but both Mg2+ and Ca2+ exerted an obvious influence on the settling of NZVI in the co-presence of HA. The settling behavior of NZVI was further examined in the co-presence of different MW fractions of HA and Ca2+. The co-presence of low MW HA fractions and Ca2+ led to a lower settling of NZVI. This might be due to the formation of a layer of HA-Ca2+ complex on the particle surface, providing stronger steric stabilization. Nevertheless, in the co-presence of high MW HA fractions and Ca2+, the settling of NZVI was initially reduced but accelerated with time, which might be due to the gradual aggregation of NZVI with time resulted from the bridging effect of HA-Ca2+ complex. [ABSTRACT FROM AUTHOR]

Aging effects play a crucial role in determining applications of green-synthesised iron-based nanoparticles in wastewater treatment from laboratory scale to practical applications. In this study, iron-based nanoparticles (Ec-Fe-NPs) were synthesised using the extract of Eichhornia crassipes and ferric chloride. Scanning electron microscopy (SEM) revealed that the fresh Ec-Fe-NPs were spherical and had a narrow particle size range (50 to 80 nm). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) demonstrated that the Ec-Fe-NPs were mainly amorphous in nature and consisted of Fe0, FeO, Fe2O3 and Fe3O4. As they aged, the particle size of the liquid Ec-Fe-NPs gradually increased and then tended to stabilise. Ec-Fe-NPs that were aged for 28 days were only 19% less efficient than fresh material at removing Cr(VI). Extracts aged up to 28 days were also tested, and their antioxidant capacity was found to be 15.4% lower than that of the fresh extracts. Furthermore, the removal efficiency of Cr(VI) using iron-based nanoparticles synthesised with the aged extracts was 67.2%. Finally, the active components of the extracts, which were responsible for the reactivity and stability of the iron-based nanoparticles, were identified by liquid chromatography–mass spectrometry. Overall, green-synthesised iron-based nanoparticles show promise for Cr(VI) removal from wastewater in practical applications. [ABSTRACT FROM AUTHOR]

Recently, nano zero-valent iron (nZVI) has emerged as an effective adsorbent for the removal of arsenic from aqueous solutions. However, its use in various applications has suffered from reactivity loss resulting in a decreased efficiency. Thus, the aim of this study was to develop an effective arsenic adsorbent as a core/shell structural nZVI/manganese oxide (or nZVI/Mn oxide) to minimize the reactivity loss of the nZVI. As the major result, the arsenic adsorption capacities of the nZVI/Mn oxide for As(V) and As(III) were approximately two and three times higher than that of the nZVI, respectively. In addition, the As(V) removal efficiency of the nZVI/Mn oxide was maintained through 4 cycles of regeneration whereas that of the nZVI was decreased significantly. The enhanced reactivity and reusability of the nZVI/Mn oxide can be successfully explained by the synergistic interaction of the nZVI core and manganese oxide shell, in which the manganese oxides participate in oxidation reactions with corroded Fe and subsequently retard the release of aqueous iron providing additional surface sites for arsenic adsorption. In summary, this study reports the successful fabrication of a core/shell nZVI/Mn oxide as an effective adsorbent for the removal of arsenic from aqueous solutions. [ABSTRACT FROM AUTHOR]

Monoethanolamine (shortly ethanolamine (ETA)), usually used as a corrosion inhibitor, is a contaminant of wastewater from the secondary cooling system of nuclear power plants (NPPs) and is not readily biodegradable. We conducted various experiments, including treatments with nano zero-valent iron (nZVI), nano-iron/calcium, and calcium oxide (nFe/Ca/CaO) with ozone (O) or hydrogen peroxide (HO) to reduce the concentration of ETA and to decrease the chemical demand of oxygen (COD) of these wastewaters. During this study, wastewater with ETA concentration of 7465 mg L and COD of 6920 mg L was used. As a result, the ETA concentration was reduced to 5 mg L (a decrease of almost 100%) and COD was reduced to 2260 mg L, a reduction of 67%, using doses of 26.8 mM of nZVI and 1.5 mM of HO at pH 3 for 3 h. Further treatment for 48 h allowed a decrease of COD by almost 97%. Some mechanistic considerations are proposed in order to explain the degradation pathway. The developed hybrid nano zero-valent iron-initiated oxidation process with HO is promising in the treatment of ETA-contaminated wastewaters. [ABSTRACT FROM AUTHOR]