Upcycling discarded polyethylene terephthalate plastics into superior tensile strength and impact resistance materials with a facile one-pot process.

Discarding PET plastic (dPET) causes serious environmental pollution and enormous fossil resources waste. Processing techniques have mainly focused on the conversion of dPET into monomers, with minimal reports highlighting their transformation into high-value materials. This work intends to transform dPET into a high-performance material with potential alternative value in harsh production environments. The soft and hard segments of the thermoplastic polyester elastomeric (TPEE) molecular structure are reacted and cross-linked with dPET using a facile one-pot process, and two main polymers, (C8H4O4)n and ((C16H18O4)0.76·(C4H8O)0.24)n are generated after the reaction. Through chemical reactions between TPEE and dPET, new characteristic products and chemical bond-crossing structures are formed, while the resulting product particles or multiple TPEE particles are anchored by the high viscosity of dPET, which endows the material with superior tensile strength (34.21 MPa) and impact resistance. The glass transition temperature (Tg) of the material implies that neither the molecular chain nor the chain segments can move, while only the atoms or groups composing the molecule vibrate at their equilibrium positions. The development of this new treatment method may contribute to the reduction of environmental pollution and the improvement of the high-value conversion and utilization of dPET.

Linking groundwater microbiome and functional ecological clusters to geogenic high hexavalent chromium from deep aquifers in a loess plateau.

Geogenic high hexavalent chromium [Cr(Ⅵ)] in groundwater is a global environmental problem. However, the groundwater microbiome and its linkage to geogenic high Cr(Ⅵ) from deep aquifers still need to be elucidated. Here, we evaluated geogenic Cr(Ⅵ), groundwater microbiome with featured functional ecological clusters and their interactive responses in groundwater from a deep aquifer in a loess plateau of Northern Shaanxi, China. We found that the compositions and structures of microbial communities in groundwater from the deep aquifer were significantly different between low Cr(Ⅵ) (LCG, < 50 µg/L) and high Cr(Ⅵ) groundwater (HCG, > 50 µg/L), with higher microbial diversity and richness in HCG (p < 0.05). Functional "specialists" related to Cr biotransformation, including Cr(Ⅵ) reducing bacteria (CRB) Rhodococcus, Nocardioides, Novosphingobium, and Acidovorax and Mn-oxidizing bacteria (MnOB) Sphingobium, and Ralstonia were positively correlated to total Cr and Cr(VI) concentrations in groundwater. Moreover, these CRB and MnOB were dominant in high Cr(VI) groundwater and associated by strong interspecific relation in an ecological cluster (p < 0.05), suggesting their indicator roles for high Cr(Ⅵ) and the contribution of MnOB mediated Cr(III) oxidation to Cr(VI) enrichment. RDA and path analysis further revealed that the geogenic Cr(Ⅵ) directly promoted the key Cr-related functional cluster with the groundwater depth, dissolved oxygen, and total dissolved solids as the cofactors indirectly influencing Cr(Ⅵ) and the functional clusters (p < 0.05). Collectively, our results highlight the significant roles of microbial ecological clusters especially functional "specialists" MnOB and CRB in groundwater Cr(Ⅵ) from deep aquifers in the loess plateau and provide a basis for sustainable management of high Cr(Ⅵ) groundwater.

Formation kinetics and reaction behavior of pentavalent chromium formed in the cement kiln co-processing of solid waste.

Cement kiln co-processing is becoming the main strategy to dispose of hazardous waste containing Cr. A newly-discovered pentavalent Cr compound, which was proved to be formed during cement kiln co-processing of solid waste, is partly responsible for the water-soluble Cr released from the cement. However, the formation characteristics and the solubility of Cr(V) are still unclear to date. In this study, the reaction kinetics and further redox reactions of Cr(V) at high temperature were examined, and its crystal structure and solubility were also explored. At the temperature range of 1000-1200 °C, the formation rate of Ca5(CrO4)3O0.5 reached over 90 % within 10 min, and then slowly increased to near 100 % from 10 min to 10 h. shows that Ca5(CrO4)3O0.5 is formed by interface reaction at an early period, and by diffusion at a later period. The kinetic analysis indicates that Ca5(CrO4)3O0.5 is initially formed through an interface reaction and subsequently through diffusion. Ca5(CrO4)3O0.5 was identified and assigned as hexagonal crystal group (P63/m). Approximately 0.55 g and 0.15 g of Ca5(CrO4)3O0.5 dissolve in neutral water at 100 °C and 50 °C, and the concentrations of Cr(V) in water reach 550 and 150 mg/L, respectively. Additionally, this study finds that at the temperature range of 400-700 °C Ca5(CrO4)3O0.5 can be oxidized into CaCrO4, and at the temperature higher than 1400 °C, it can be further converted into Ca3(CrO4)2 and reduced into CaCr2O4. This study gives a deep insight into Cr oxidation-reduction reaction during thermal treatment of solid waste. These insights provide a comprehensive understanding of Cr oxidation-reduction reactions during the thermal treatment of solid waste, offering valuable guidance for waste management strategies.

Hydrogeological controls on chromium enrichment along the groundwater flow path in the Baiyangdian Catchment, North China Plain.

Although the natural occurrence of high chromium (Cr) groundwater has been intensively investigated in bedrock or sedimentary aquifers, the impacts of hydrogeological conditions on dissolved Cr distribution are poorly understood. In this study, groundwater samples from recharge mountain area (Zone I) through runoff area (Zone II) to discharge area (Zone III) were taken from bedrock and sedimentary aquifers approximately along the flow path in Baiyangdian (BYD) catchment, China, to reveal how hydrogeological conditions and hydrochemical evolution contributed to Cr enrichment in groundwater. Results showed that dissolved Cr was dominated by Cr(VI) species (>99 %). Around 20 % of studied samples had Cr(VI) exceeding 10 µg/L. Groundwater Cr(VI) was of natural origin, which generally increased along the flow path, and high concentrations (up to 80.0 µg/L) were observed in deep groundwater of Zone III. At the local scales, geochemical processes including silicate weathering, oxidation, and desorption under weakly alkaline pH, predominately contributed to Cr(VI) enrichment. Principal component analysis showed that oxic conditions were the principal control of Cr(VI) in Zone I, and geochemical processes (especially Cr(III) oxidation and Cr(VI) desorption) predominantly enhanced groundwater Cr(VI) enrichment in Zones II and III. However, at the regional scale, Cr(VI) enrichment was dominantly facilitated by the low flow rate and recharge of paleo-meteoric water due to the long-term water-rock interaction in the BYD catchment.

Genesis of high hexavalent chromium groundwater in deep aquifers from loess plateau of Northern Shaanxi, China.

Hexavalent chromium (Cr(VI)) groundwater usually exists in shallow aquifers related to ultramafic and serpentine formations, but knowledge of the genesis of dissolved Cr(VI) in deep sandstone aquifers is limited. Both groundwater and aquifer sediments were taken from the Jingbian County in the Loess Plateau of Northwestern Shaanxi to investigate distribution and genesis mechanism of high Cr(VI) groundwater in deep sandstone aquifers. Results showed that the Cr concentrations (median 142 µg/L) in groundwater from deep aquifers (>100 m) were relatively high, while the Cr concentrations in shallow groundwater were low (median 33.8 µg/L). Dissolved Cr mainly existed in the species of Cr(VI) (average, 90%). Deep groundwater with higher Cr(VI) concentrations generally had higher pH, Eh, and DO than shallow groundwater, indicating that the high Cr(VI) groundwater existed in relatively oxic environment. Cretaceous sandstones in deep aquifers had anomalously high contents of total Cr (average 115 mg/kg), where Cr was mainly present in silicates-bound form, and secondly in strongly adsorbed form. There were positive correlations between Mn and Cr in the unweathered silicate-bound form and adsorbed form, which were conducive to Cr(III) oxidation into Cr(VI) in an alkaline-oxic environment. The different ionic ratios (i.e. (Ca2+ + Mg2+)/(HCO3- + SO42-)) also supported silicate weathering as the dominant rock-water interactions in the deep groundwater, which enhanced the release of the unweathered silicate-bound Cr. Relatively high pH and ionic strength mobilized the adsorbed Cr(VI) into groundwater. This investigation emphasizes the geological origin of high Cr(VI) groundwater in deep sandstone aquifers containing Mn oxides, which deserves more concerns for the purpose of drinking water supply.

Boosting photocatalytic reduction of nitrate to ammonia enabled by perovskite/biochar nanocomposites with oxygen defects and O-containing functional groups.

Photocatalytic ammonia synthesis from waste nitrate has emerged as a promising strategy in water treatment; however, the conversion and selectivity still remain a great challenge. Herein, recyclable magnetic perovskite (LaFeO3)/biochar nanocomposites were successfully synthesized by the co-pyrolysis of the lotus biomass and Fe/La salts without extra organic complexants. Results showed that the lotus interacted with the iron ions (Fe3+) and the lanthanum ions (La3+) changing the surface and structural characteristics of catalysts. Oxygen defects of LaFeO3 were enhanced due to biomass introduction, which accelerated the separation of electron-hole pairs. On the other hand, Fe/La salts participated in the modification process of the biochar surface during the carbonization, which promoted the exposure of oxygen-containing functional groups and aromatic structures facilitating the nitrate adsorption. Notably, the redox-active quinone/phenol groups on the biochar surface contributed to the photogenerated electrons exchange favoring the ammonium ion (NH4+) selectivity as direct electron donor. Nitrate conversion reached 98% and ammonia selectivity reached 97% over the LaFeO3/biochar photocatalyst under visible light irradiation, when the mass ratio of lotus and Fe/La salts was optimized. Our findings may potentially provide a green and cost-effective way for ammonia recovery from nitrate contaminants.

Oxidation behavior of Cr(III) during thermal treatment of chromium hydroxide in the presence of alkali and alkaline earth metal chlorides.

The oxidation behavior of Cr(III) during the thermal treatment of chromium hydroxide in the presence of alkali and alkaline earth metal chlorides (NaCl, KCl, MgCl2, and CaCl2) was investigated. The amounts of Cr(III) oxidized at various temperatures and heating times were determined, and the Cr-containing species in the residues were characterized. During the transformation of chromium hydroxide to Cr2O3 at 300 °C approximately 5% of the Cr(III) was oxidized to form intermediate compounds containing Cr(VI) (i.e., CrO3), but these intermediates were reduced to Cr2O3 when the temperature was above 400 °C. Alkali and alkaline earth metals significantly promoted the oxidation of Cr(III) during the thermal drying process. Two pathways were involved in the influences the alkali and alkaline earth metals had on the formation of Cr(VI). In pathway I, the alkali and alkaline earth metals were found to act as electron transfer agents and to interfere with the dehydration process, causing more intermediate Cr(VI)-containing compounds (which were identified as being CrO3 and Cr5O12) to be formed. The reduction of intermediate compounds to Cr2O3 was also found to be hindered in pathway I. In pathway II, the alkali and alkaline earth metals were found to contribute to the oxidation of Cr(III) to form chromates. The results showed that the presence of alkali and alkaline earth metals significantly increases the degree to which Cr(III) is oxidized during the thermal drying of chromium-containing sludge.

The role of temperature on Cr(VI) formation and reduction during heating of chromium-containing sludge in the presence of CaO.

In this study, the temperature dependence of Cr(VI) formation and reduction in the presence of CaO was examined during the thermal treatment of sludge that contains chromium. thermogravimetry-differential scanning calorimetry and X-ray diffractometry were used to characterize the thermal behavior and phase transformation, respectively. Na2CO3 leaching procedure was employed to determine the amount of Cr(VI). The result showed that CaO promoted Cr(III) oxidation, however, its influence is very dependent on heating temperature, with the extent of the effect varying with temperature. From 200-400 °C, the presence of CaO facilitated formation of intermediate product Cr2O3+x containing Cr(VI) during dehydration of chromium hydrate, while Cr2O3+x would decompose as temperature over 400 °C, accompanied by part of Cr(VI) being reduced to Cr(III). From 500 to 900 °C, Cr(III) reacted with CaO to form a leachable CaCrO4 product. This product was stable and a prolonged heating time did not reduce the amount of Cr(VI) significantly. At 1000-1200 °C, part of CaCrO4 was reduced to Ca(CrO2)2 in 1h. While extended heating time above 1h resulted in the Ca(CrO2)2 being oxidized reversibly to CaCrO4 at 1200 °C. Since CaCrO4 is thermodynamically less stable over 1000 °C, MgO could induce CaCrO4 to be reduced into MgCr2O4 at around 900 °C, lower than that for the reduction from CaCrO4 into Ca(CrO2)2. It suggested that adding MgO might be a potential approach for inhibiting Cr(VI) formation during heating sludge containing chromium.

Hydrothermal synthesis and characterization of aluminum-free Mn-ß zeolite: a catalyst for phenol hydroxylation.

Zeolite beta, especially heteroatomic zeolite beta, has been widely used in the industries of fine chemicals and petroleum refining because of its outstanding thermal stability, acid resistance, and unique 3-D open-frame structure. In this paper, aluminum-free Mn-ß zeolite was hydrothermally synthesized in the SiO2-MnO2-(TEA)2O-NaF-H2O system. The effect of the chemical composition of the precursor mixture to the crystallization of the Al-free Mn-ß zeolite was investigated. The synthesized Al-free Mn-ß zeolite was characterized by inductively coupled plasma (ICP), XRD, thermogravimetric/differential thermal analysis (TG/DTA), N2 adsorption-desorption, FT-IR, UV-vis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The results show that the synthesized zeolite has a structure of ß zeolite with good crystallinity and Mn ions present in the framework of the zeolite. The synthesized Al-free Mn-ß zeolite shows great catalytic activity toward the phenol hydroxylation reaction using H2O2 as the oxidant. Approximately 35% of phenol conversion and ∼98% of dihydroxybenzene selectivity can be obtained under the optimal conditions.