Different effects of surface heterogeneous atoms of porous and non-porous carbonaceous materials on adsorption of 1,1,2,2-tetrachloroethane in aqueous environment

Biochar-derived organic carbon promoting the dehydrochlorination of 1,1,2,2-tetrachloroethane and its molecular size effects: Synergies of dipole-dipole and conjugate bases

The environmental effects of biochar-derived organic carbon (BDOC) have attracted increasing attention. Nevertheless, it is unknown how BDOC might affect the natural attenuation of widely distributed chloroalkanes (e.g., 1,1,2,2-tetrachloroethane (TeCA)) in aqueous environments. We firstly observed that the kinetic constants (ke) of TeCA dehydrochlorination in the presence of BDOC samples or their different molecular size fractions (<1 kDa, 1∼10 kDa, and >10 kDa) ranged from 9.16×103 to 26.63×103 M-1h-1, which was significantly greater than the ke (3.53×103 M-1h-1) of TeCA dehydrochlorination in the aqueous solution at pH 8.0, indicating that BDOC samples and their different molecular size fractions all could promote TeCA dehydrochlorination. For a given BDOC sample, the kinetic constants (ke) of TeCA dehydrochlorination in the initial pH 9.0 solution was 2∼3 times greater than that in the initial pH 8.0 solution due to more formation of conjugate bases. Interestingly, their DOC concentration normalized kinetic constants (ke/[DOC]) were negatively correlated with SUVA254, and positively correlated with A220/A254 and the abundance of aromatic protein-like/polyphenol-like matters. A novel mechanism was proposed that the CH dipole of BDOC aliphatic structure first bound with the CCl dipole of TeCA to capture the TeCA molecule, then the conjugate bases (-NH-/-NH2 and deprotonated phenol-OH of BDOC) could attack the H atom attached to the β-C atom of bound TeCA, causing a CCl bond breaking and the trichloroethylene formation. Furthermore, a fraction of >1 kDa had significantly greater ke/[DOC] values of TeCA dehydrochlorination than the fraction of <1 kDa because >1 kDa fraction had higher aliphiticity (more dipole-dipole sites) as well as more N-containing species and aromatic protein-like/polyphenol-like matters (more conjugate bases). The results are helpful for profoundly understanding the BDOC-mediated natural attenuation and fate change of chloroalkanes in the environment.

Fractionation of biomass-burning smoke-derived dissolved organic matters on the surface of clay minerals: Variations of molecular properties and components

Biomass burning (e.g., wildfire) frequently occurs globally, inevitably produces abundant biomass-burning smoke-derived dissolved organic matters (BBS-DOMs) which eventually deposits on the surface environment. The adsorption and fractionation of BBS-DOMs on clays inevitably alter their biogeochemical process and environmental behaviors in the surface environment. It is therefore important to clarify the adsorption and fractionation of BBS-DOM on clay surfaces. This study found that the fractionation of BBS-DOMs on clays (montmorillonite and kaolinite) were controlled by their functional groups, aromaticity, molecular size and organic components. The spectral indexes (SUVA254 and S275-295) of BBS-DOMs in solution after clays adsorption suggested that with the increasing DOC concentration, the primary interaction between BBS-DOMs and clays changed from hydrogen bond to hydrophobic/pore filling effects, and the adsorption ratio of the large molecules increased, which were very different from natural fulvic acid. Furthermore, various BBS-DOMs and fulvic acid had different component fractionation behaviors during clay adsorption, because they had different abundances of protein-like matters (hydrogen bond donors), pyridine-N/pyrimidine-N (positive charge doners of electrostatic interaction), and fulvic-like matters (hydrophobic interaction and pore filling effect). Additionally, the increasing pH weakened the adsorption of bulk BBS-DOMs and enhanced the adsorption ratio of aromatic matters and smaller BBS-DOM molecules. Meanwhile, at a higher pH, the adsorption ratio of protein-like matters increased, while the adsorption ratio of humic- and fulvic-like matters decreased. The result was ascribed to the enhanced hydrogen bond between protein-like matters and clays as well as the enhanced electrostatic repulsion between humic-/fulvic-like matters and clays. This study is helpful for deeply understanding the multimedia-crossing environmental behavior of BBS-DOMs in the surface environment.

Preparation and Performance of Carbon-Based Ce-Mn Catalysts for Efficient Degradation of Acetone at Low Temperatures

Based on the porous carbon material from citric acid residue, catalysts of different Ce-Mn ratios were prepared with incipient-wetness impregnation (IWI) to delve into their acetone-degrading performance and relevant mechanisms. When the Ce-Mn molar ratio is 0.8, the prepared catalyst Ce_0.8-Mn/AC shows abundant and uniformly dispersed Mn and Ce particles on the surface. The content of Mn and Ce on the Ce_0.8-Mn/AC surface reaches 5.64% and 0.75%, respectively. At the acetone concentration of 238 mg/m³ (100 ppm), the laws of acetone degradation in different catalysts at different catalyzing temperatures and with various oxygen concentrations were studied, and we found that the rate of acetone degradation by Ce_0.8-Mn/AC can exceed 90% at 250 °C. Cerium oxide and manganese oxide are synergistic in the catalytic degradation of acetone. Adding cerium to manganese-based catalysts can increase the oxygen migration rate in the catalysts and thus raise the reduction rate of lattice oxygen in manganese oxide. The results offer new ideas and approaches for the efficient and comprehensive utilization of bio-fermentation by-products, and for the development of cheap and high degradation performance catalysts for acetone.

Sorption of naphthalene and 2-naphthol onto porous carbonaceous materials as a function of pore size, metals, and oxygen-containing groups

The important role of oxygen-containing groups of porous carbonaceous materials (PCMs) on sorption of organic compounds has been realized, but whether these groups can generate different joint effects, especially when oxidized PCMs with different pore sizes are complexed with heavy metals (Cu²⁺), remains ambiguous. The present study aimed to determine how pore sizes, metal ions, and oxygen-containing groups as a function affect the sorption of naphthalene and 2-naphthol to PCMs (e.g., activated carbons/ACs and mesoporous carbon/CMK-3). The H₂-reduced oxidized PCMs were used as the control of low oxygen content to avoid changes in the pore structure properties compared with the oxidized PCMs. Oxygen-containing groups considerably decreased the sorption of naphthalene and 2-naphthol to PCMs because of their weaker hydrophobic interaction and fewer sorption sites. Notably, naphthalene sorption on oxidized AC was inhibited with Cu²⁺ because of the steric constraint of Cu²⁺ hydration shells of the micropores. However, pore blockage by Cu²⁺ reduced the mesopore size of oxidized CMK-3, leading to enhanced pore filling effect and cation-π bonding, and therefore increased naphthalene sorption. For 2-naphthol, the sorption to oxidized PCMs initially increased and then decreased with increasing Cu²⁺ concentration attributed to the fewer Cu²⁺ acting as a bridging agent and excess Cu²⁺ competing for sorption sites.

Differential roles of ash in sorption of triclosan to wood-derived biochars produced at different temperatures

Biochar is composed of carbonaceous and inorganic (ash) fractions. The structural properties of carbonaceous fractions and the composition of ash in biochar are both variable with pyrolysis temperature. However, it is unknown whether ash may play different roles in sorption of organic compounds to the carbonaceous fraction of biochars produced at different temperatures. Hence, in this study, the pristine biochars produced at 300-900°C and their corresponding deashed biochars were investigated, and the combined roles of carbonaceous fraction and ash in sorption of triclosan were compared. The results showed that the biochars produced at 300-400°C had high content of uncarbonized organic structure with dominating partition effect. The combination of uncarbonized organic structure and ash had comparable or even higher sorption coefficient (K_D ) for triclosan at low concentration compared with a single uncarbonized organic structure. However, for the biochars produced at 600-900°C, which were mainly composed of carbonized or graphitized carbon structure, ash had significant effect on triclosan sorption by reducing surface adsorption and pore filling effect. The combination of carbonaceous fraction and ash decreased K_D values for triclosan at any tested concentrations. In addition, the results of pH effect on sorption indicated that ash possibly decreased the electrostatic repulsion of deprotonated phenolic hydroxyl between biochars and triclosan. Accordingly, it will be more valuable to design biochars for pollutant sorption from the perspective of combined role of carbonaceous fraction and ash rather than a single role of carbonaceous fraction.

Insights into the roles of the morphological carbon structure and ash in the sorption of aromatic compounds to wood-derived biochars

Currently, it is still lack of systematic and in-depth knowledge regarding the co-effect of carbon-based fractions and ash in the sorption behavior of biochars. Therefore, pristine wood-derived biochars (PBCs) produced at different temperatures and their corresponding de-ashed versions (DBCs) were used to determine the roles of carbon's morphological structure and ash in sorption of aromatic compounds (toluene, m-toluidine, and m-nitrotoluene) to biochars. The results showed that biochars produced at 300-400 °C (mainly uncarbonized organic matter, UCOM) and 900 °C (turbostratic carbon, TC) may have stronger partition effect and pore filling effect with π-π interaction, respectively, and thus have greater sorption coefficients (Lg K_d) than biochars produced at 600 °C (pyrogenic amorphous carbon, PAC), which are probably dominated by surface hydrophobic effect. Meanwhile, TC had a greater Lg K_d than UCOM at low adsorbate concentrations (C_e), but exhibited an opposite trend at high C_e. The Lg K_d values of DBCs are always greater than those of PBCs, indicating ash has an inhibitory effect on sorption of aromatic compounds to biochars. Furthermore, the role of ash in sorption behavior of PBCs would vary with solution pH. At a neutral pH, PBCs have the maximum sorption quantity for aromatic compounds due to the formed cation-π bond between cations of ash and aromatic compounds. However, the acidic pH enhanced the dissolution of cations in ash and the basic pH enhanced the hydroxylation of cations in ash. Therefore, both acidic and basic pH weakened the cation-π bond between ash and aromatic compounds and decreased the sorption of aromatic compounds on PBCs. The results suggest that de-ashed biochars with more UCOM or TC are effective sorbents for sequestration of aromatic compounds, and provide a well-designed method for improving the sorption efficiency of biochars.

Unraveling sorption of nickel from aqueous solution by KMnO4 and KOH-modified peanut shell biochar: Implicit mechanism

Nickel-containing wastewater is a serious hazard to water environment, so that it is a burning issue to find an efficient and environment-friendly adsorbent. The conventional biochar could not effectively adsorb nickel (Ni(II)), so our study focuses on exploring the adsorption of chemically modified biochar to Ni(II). In this study, the biochar derived from waste peanut shell was modified by KMnO₄ and KOH (MBC). And a series of experiment were carried out to evaluate the sorption ability and explore adsorption mechanism of modified biochar to Ni(II). The results showed the adsorption ability of MBC to Ni(II) reached 87.15 mg g^-1. And the reaction process was spontaneous and endothermic chemisorption. Meanwhile, the analysis of FTIR and XPS visually revealed that the amine groups in the modified biochar could form NH₂Ni with Ni(II) by complexation, while the hydroxyl could form nickel hydroxide and complexed nickel oxide by co-precipitation and complexation. This research showed this novel MBC is a promising adsorbent and has a fantastic prospect in the application of nickel-containing wastewater.

Sorption of chlorinated hydrocarbons to biochars in aqueous environment: Effects of the amorphous carbon structure of biochars and the molecular properties of adsorbates

Currently, the role of amorphous carbon structure (ACS) in sorption of chlorinated hydrocarbons (CHs) to biochars remains little known. Therefore, three CHs (1,1,2,2-tetrachloroethane, 1,3,5-trichlorobenzene and γ-hexachlorocyclohexane) with different molecular properties were selected as model adsorbates to investigate the effect of ACS on sorption of CHs to biochars produced at seven different pyrolysis temperatures (300-900 °C). There were two main mechanisms for ACS controlling the sorption of CHs. First, the polar sites on ACS are hydrophilic, CHs with greater polarity could strongly compete with the water molecule for the hydrophilic sites. Second, ACS of low temperature (300-400 °C) produced biochars possessing the natural organic matter (NOM)-like structure occupied some hydrophobic sites on condensed graphitic structure (CGS) of biochars. CHs with great hydrophobicity possibly seized the hydrophobic sorption sites on CGS from the NOM-like structure. Therefore, ACS of biochar was more benefit for sorption of strong polar CHs (1,1,2,2-tetrachloroethane: π^∗ = 0.95; LogK_ow = 2.39) or strong hydrophobic CHs (1,3,5-trichlorobenzene: π^∗ = 0.70; LogK_ow = 4.19) than CHs (γ-hexachlorocyclohexane: π^∗ = 0.68; LogK_ow = 3.72) with relatively low polarity and hydrophobicity. The result reflects that the interaction between NOM and natural black carbon/biochars in soil and water environment possibly plays the similar role in controlling the environmental behavior of various polar or hydrophobic organic pollutants. Moreover, with increasing concentration of adsorbate (C_e), the first mechanism enhanced, while the second mechanism weakened. This study gives a deep insight into the roles of ACS of biochars in controlling the fate and availability of CHs with different molecular properties in environment.

Facile synthesis of graphitic C3N4 nanoporous-tube with high enhancement of visible-light photocatalytic activity

A simple and convenient method was used to synthesize a graphitic carbon nitride (g-C₃N₄) nanoporous-tube by using SiO₂ nanoparticles as pore formers. The structure of the g-C₃N₄ nanoporous-tube was characterized by the SEM and TEM images. Taking photodegradation of RhB as an example, the photocatalytic activity of the as-prepared g-C₃N₄ nanoporous-tube was investigated. It can photodegrade 90% RhB in 40 min under visible-light irradiation and obtain a k value of 0.04491 min^-1, which is 8.16 times that of bulk g-C₃N₄, 3.09 times that of tubular g-C₃N₄ and 1.48 times that of tubular g-C₃N₄-SiO₂. The significant enhancement in photocatalytic efficiency is due to the edge effect of the pores and the special structure of the tubes. In addition, the possible mechanism of photocatalytic degradation of RhB was also proposed based on the trapping experiment of active species, which indicated that the superoxide radicals ([Formula: see text]) and the holes (h ⁺) were the main reactive species in this photocatalyst. This work may open up a new idea of innovation in g-C₃N₄ structure and inspire its follow-up study.