Boosting nitrogen fertilization by a slow releasing nitrate-intercalated biocompatible layered double hydroxide–hydrogel composite loaded with Azospirillum brasilense

Indiscriminate use of chemical fertilizers leads to soil environmental disbalance and therefore, preparation and application of environment-friendly slow-release multifunctional fertilizers are of paramount importance for sustainable crop production in the present scenario. In this study, we propose a slow-release multifunctional composite nitrogen (N) fertilizer, which possesses the ability to supply plant accessible N in the form of ammonium (NH₄⁺) and nitrate (NO₃⁻) to improve nitrate assimilation coupled with zinc (Zn, a major micronutrient for plants in the soil) after its degradation. For this purpose, NO₃⁻-intercalated zinc–aluminum (Zn–Al) layered double hydroxide (LDH) was synthesized using a co-precipitation protocol. The prepared LDH was added as 25.45% of total polymer weight to a sodium carboxymethyl cellulose/hydroxyethyl cellulose citric acid (NaCMC/HEC-CA) biodegradable hydrogel. A. brasilense, commonly used nitrogen-fixing bacteria in soils, was added to the LDH–hydrogel composite along with LDH alone to augment the availability of NH₄⁺ and NO₃⁻. Adjusting the pH under acidic (pH 5.25) and neutral (pH 7) conditions, the release pattern of NO₃⁻ from LDH and the composite was monitored for 30 days at normal temperature. The pH was selected based on the soil analysis data of North East India. The LDH-composite released 90% (w/w) and 85.45% (w/w) of intercalated NO₃⁻ at pH 5.25 and 7.00 respectively in 30 days. However, 100% (w/w) and 87% (w/w) of intercalated NO₃⁻ at pH 5.25 and 7.00 respectively were released in 30 days when only LDH was applied, which indicated the lower performance of LDH alone in comparison to the LDH-composite for the nitrate holding pattern. The pH of the bacteria-loaded system was observed to be acidic (pH = 5–6) during the study of nitrate assimilation and Zn²⁺ release. A. brasilense improved nitrate assimilation and increased the NH₄⁺ ion concentration in the studied system. A significant increase in Zn²⁺ release was observed from day 5 in the presence of A. brasilense in the LDH-composite compared with that in the absence of A. brasilense. In conclusion, the prepared LDH–hydrogel–A. brasilense composite fertilizer system increases the availability of plant accessible N form (both NO₃⁻ and NH₄⁺) and can potentially improve soil fertility with the addition of Zn and bacteria to the soil in the extended course.

Indiscriminate use of chemical fertilizers leads to soil environmental disbalance, therefore, use of environment-friendly slow-release multifunctional fertilizers are of paramount importance for sustainable crop production in the present scenario.     

Extraction of polyoxotantalate by Mg–Fe layered double hydroxides: elucidation of sorption mechanisms

The extraction of Ta(v) as polyoxometallate species (H_xTa₆O₁₉^(8−x)−) using Mg–Fe based Layered Double Hydroxide (LDH) was evaluated using pristine material or after different pre-treatments. Thus, the uptake increased from 100 ± 5 mg g⁻¹ to 604 ± 30 mg g⁻¹, for respectively the carbonated LDH and after calcination at 400 °C. The uptake with calcined solid after its reconstruction with Cl⁻ or NO₃⁻ anions has also been studied. However, the expected exchange mechanism was not found by X-ray Diffraction analysis. On the contrary, an adsorption mechanism of Ta(v) on LDH was consistent with measurements of zeta potential, characterized by very negative values for a wide pH range. Moreover, another mechanism was identified as the main contributor to the uptake by calcinated LDH, even after its reconstruction with Cl⁻ or NO₃⁻: the precipitation of Ta(v) with magnesium cations released from MgO formed by calcination of the LDH. This latter reaction has been confirmed by the comparison of the uptake of Ta(v) in dedicated experiments with solids characterized by a higher magnesium solubility (MgO and MgCl₂). The obtained precipitate has been analyzed by X-ray diffraction (XRD) and would correspond to a magnesium (polyoxo)tantalate phase not yet referenced in the powder diffraction databases.

Reaction of polyoxotantalate ions and MgFe Layered Double Hydroxide leads to magnesium polyoxotantalate precipitate.     

Structure and mechanical behavior of in situ developed Mg2Si phase in magnesium and aluminum alloys – a review

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades. Magnesium and aluminum alloys are very suitable candidate materials. Research on alloys with an Mg₂Si phase started about three decades ago. The current scenario is that magnesium and aluminum alloys containing an Mg₂Si phase are very popular in the scientific community and extensively used in the automotive and aerospace industries. Mg₂Si is a very stable phase and exhibits excellent mechanical, thermal, electrochemical and tribological properties. This paper presents a brief review of Mg–Si binary alloys, and Mg–Si–Al and Al–Si–Mg alloys. Grain refinement methods and mechanical properties have been reported on lightweight alloys containing Mg and Si. The available results show that silicon reacts with magnesium and forms an intermetallic compound with the stoichiometric formula Mg₂Si. There is in situ formation of an Mg₂Si phase in Mg–Si, Mg–Si–Al and Al–Mg–Si alloys by the diffusion or precipitation process. The morphology and size of an in situ developed Mg₂Si phase depend on the synthesis route and base metal or matrix. In the liquid metallurgy process the precipitation sequence depends on the cooling rate. The morphology of the Mg₂Si phase depends on the precipitation sequence and the mechanical properties depend on the morphology and size of the Mg₂Si phase within the alloy matrix.

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades.     

Synthesis of biodiesel from waste cooking oil catalyzed by β-cyclodextrin modified Mg–Al–La composite oxide

In this study, Mg–Al–La composite oxide loaded with ionic liquid [Bmim]OH was used as a catalyst for the synthesis of fatty acid isobutyl ester (FAIBE) via transesterification between waste cooking oil and isobutanol. Mg–Al–La composite oxide was synthesized from the β-cyclodextrin (β-CD) intercalation modification of Mg–Al–La layered double hydroxides. The structure of the catalyst was characterized via XRD, BET and EDS. The results showed that the interlayer space of the catalyst was increased due to β-CD intercalation modification. The IL/CD–Mg–Al–La catalyst exhibited significant catalytic activity and regeneration performance in transesterification due to large interlayer space and strongly alkaline ionic liquid. The yield of FAIBE achieved was 98.3% under the optimum reaction condition and 95.2% after regeneration for six times. The viscosity–temperature curve of FAIBE was determined and the phase transition temperature was −1 °C. The pour point of FAIBE was only −10 °C, which exhibited excellent low temperature fluidity.

In this study, Mg–Al–La composite oxide loaded with ionic liquid [Bmim]OH was used as a catalyst for the synthesis of fatty acid isobutyl ester (FAIBE) via transesterification between waste cooking oil and isobutanol.     

Evaluation of a novel low-carbon to nitrogen- and temperature-tolerant simultaneously nitrifying–denitrifying bacterium and its use in the treatment of river water

In this study, a simultaneously heterotrophic nitrifying–aerobic denitrifying bacterium, designated KSND, was newly isolated from a lake wetland. Its removal efficiencies for 160 mg L⁻¹ ammonium, 105 mg L⁻¹ nitrate, and 8.39 mg L⁻¹ nitrite were 86.56%, 74.52%, and 100% in 24 h, with removal rates of 5.77 mg L⁻¹ h⁻¹ for NH₄⁺–N, 3.26 mg L⁻¹ h⁻¹ for NO₃⁻–N, and 0.35 mg L⁻¹ h⁻¹ for NO₂⁻–N. The bacterium retained ∼63% of its maximal removal rate at 10 °C and 56% of its maximal removal rate at a carbon to nitrogen (C/N) ratio of 4 : 1, with no nitrite accumulation. Gene-specific PCR indicated the absence of the key genes for nitrification and denitrification, encoding hydroxylamine oxidoreductase and nitrite reductase, respectively, suggesting that KSND achieves effective nitrogen removal by another pathway. KSND was used to treat river wastewater by culturing it in a floating bed bioreactor. Ammonia nitrogen decreased significantly from 8.76 mg L⁻¹ initially to 1.87 mg L⁻¹ in 90 days, with no NO₃⁻–N or NO₂⁻–N toxicants, indicating the great potential utility of KSND in future full-scale applications in the treatment of low-C/N wastewater.

A novel simultaneous nitrification and denitrification Klebsiella sp. exhibits high nitrogen removal efficiency under low-temperature and low C/N wastewater.     

Synergistic and simultaneous biosorption of phenanthrene and iodine from aqueous solutions by soil indigenous bacterial biomass as a low-cost biosorbent

The removal of phenanthrene and iodine from aqueous solutions in single and binary systems by inactivated soil indigenous bacterial biomass (SIBB), as well as affecting factors, were evaluated. Sorption kinetic and isotherm studies were carried out to investigate the synergistic effects of phenanthrene and iodine. Optimal parameters for the biosorption process included a solution pH of 6.0 and biosorbent dosage of 0.75 g L⁻¹. The ionic strength significantly decreased the biosorption of both phenanthrene and iodine in single conditions, while no obvious influences were found in the binary conditions. A pseudo-second-order model was well fitted to the kinetic biosorption data for both phenanthrene and iodine. The results showed that the presence of co-solute accelerated the biosorption processes and the pseudo-second-order biosorption rates (k₂) for phenanthrene and iodine increased from 0.005441 to 0.009825 g mg⁻¹ min⁻¹ and from 0.000114 to 0.000223 g mg⁻¹ min⁻¹, respectively. The SIBB showed strong affinity with both phenanthrene and iodine, with a partition coefficient K_d (Linear model) of 6892.4 L kg⁻¹ for phenanthrene and affinity parameter K_L (Langmuir model) of 232 500 L kg⁻¹ for iodine. The presence of co-solute illustrated a synergistic effect on the biosorption of phenanthrene and iodine due to intermolecular forces between phenanthrene and iodine, enhancing the K_d of 34.7% for phenanthrene and K_L of 107.0% for iodine, respectively. The results suggested that SIBB was an effective material for the simultaneous biosorption of phenanthrene and iodine from aqueous solutions.

Co-solute significantly enhanced the sorption affinity of phenanthrene and iodine by bacterial biomass.     

Combing δ15N and δ18O to identify the distribution and the potential sources of nitrate in human-impacted watersheds,Shandong, China

Identifying the anthropogenic and natural sources of nitrate emissions contributing to surface water continues to be an enormous challenge. It is necessary to control the water quality in the watershed impacted by human disturbance. In this study, water chemical parameters including nitrate (NO₃⁻) concentrations, δ¹⁵N–NO₃⁻, δ¹⁸O–NO₃⁻, and δ¹⁸O–H₂O were analyzed to investigate the contamination and sources of NO₃⁻ in two watershed rivers (Jinyun, JYN and Jinyang, JYA), Jinan, Shandong, China. Results indicated NO₃⁻ concentrations in the JYN were significantly higher than those in the JYA (P < 0.05), probably because of high N input of the extensive farmlands or orchards in the drainage basin. δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻, associated with Cl⁻, indicated that nitrate-nitrogen (NO₃⁻–N) was not derived from atmospheric deposition but came principally from manure/sewage and soil organic matter in these two watersheds. The microbial nitrification took place in the nitrate of manure/sewage and soil nitrate. The combination of NO₃⁻ concentration and nitrogen and oxygen isotope suggested that NO₃⁻ had undergone microbial denitrification after entering the rivers. Furthermore, NO₃⁻ concentrations had significant temporal and spatial variation highlighting differential sources and fates. These results expand our understanding of mechanisms driving NO₃⁻ retention and transport and provide strategies in managing NO₃⁻ contamination in different land use watersheds around the world.

NO₃⁻ showed seasonal and spatial patterns in two human-impacted watersheds. NO₃⁻ is primarily from manure/sewage according to δ¹⁵N and δ¹⁸O. Microbial nitrification took place in the NO₃⁻ of manure/sewage and soil nitrate.     

Inhibition effect of ZrF4 on UO2 precipitation in the LiF–BeF2 molten salt

The dissolution–precipitation behavior of zirconium dioxide (ZrO₂) in molten lithium fluoride–beryllium fluoride (LiF–BeF₂, (2 : 1 mol, FLiBe)) eutectic salt at 873 K was studied. The results of the dissolution experiment showed that the saturated solubility of ZrO₂ in the FLiBe melt was 3.84 × 10⁻³ mol kg⁻¹ with equilibrium time of 6 h, and its corresponding apparent solubility product (K′_sp) was 3.40 × 10⁻⁵ mol³ kg⁻³. The interaction between Zr(iv) and O²⁻ was studied by titrating lithium oxide (Li₂O) into the FLiBe melt containing zirconium tetrafluoride (ZrF₄), and the concentration of residual Zr(iv) in the melt gradually decreased due to precipitate formation. The precipitate corresponded to ZrO₂, as confirmed by the stoichiometric ratio and X-ray diffraction analysis. The K′_sp was 3.54 × 10⁻⁵ mol³ kg⁻³, which was highly consistent with that from the dissolution experiment. The obtained K′_sp of ZrO₂ was in the same order of magnitude as that of uranium dioxide (UO₂), indicating that a considerable amount of ZrF₄ could inhibit the UO₂ formation when oxide contamination occurred in the melt containing ZrF₄ and uranium tetrafluoride (UF₄). Further oxide titration in the LiF–BeF₂–ZrF₄ (5 mol%)–UF₄ (1.2 mol%) system showed that ZrO₂ was formed first with O²⁻ addition less than 1 mol kg⁻¹, and the precipitation of UO₂ began only after the O²⁻ addition reached 1 mol kg⁻¹ and the precipitation of ZrO₂ decreased the ZrF₄ concentration to 0.72 mol kg⁻¹ (3 mol%). Lastly, UO₂ and ZrO₂ coprecipitated with further O²⁻ addition of more than 1 mol kg⁻¹. The preferential formation of ZrO₂ effectively avoided the combination of UF₄ and O²⁻. This study provides a solution for the control of UO₂ precipitation in molten salt reactors.

This study provides an effective solution for controlling and monitoring the nuclear fuel precipitation (UO₂) in molten fluorides, which is of great importance for the safe operation and fuel salt design of molten salt reactor (MSR).     

Efficient in situ generation of H2O2 by novel magnesium–carbon nanotube composites

Hydrogen peroxide (H₂O₂) is widely employed as an environmentally friendly chemical oxidant and an energy source. In this study, a novel magnesium–carbon nanotube composite was prepared by a ball milling process in argon atmosphere using polyvinylidene fluoride (PVDF) as a binder. The resulting material was then tested for the in situ generation of H₂O₂. The preparation and operation conditions of the composite were systemically investigated and analyzed to improve the efficiency of the in situ generation of H₂O₂. Under the optimized conditions, while aerating with oxygen for 60 min, a maximum H₂O₂ concentration of 194.73 mg L⁻¹ was achieved by the Mg–CNTs composite prepared using Mg : CNT : PVDF with a weight ratio of 5 : 1 : 2.4. In the Mg–CNTs/O₂ system, dissolved oxygen molecules were reduced to H₂O₂, while magnesium was oxidized owing to the electrochemical corrosion. In addition, a part of dissolved magnesium ions converted into magnesium hydroxide and precipitated as nanoflakes on the surfaces of CNTs. A mechanism was proposed, suggesting that the formation of a magnesium/carbon nanotubes corrosion cell on the Mg–CNT composite promoted the in situ synthesis of H₂O₂. Overall, this study provides a promising and environmentally friendly strategy to fabricate magnesium/CNT composites for the in situ generation of H₂O₂, which could be applied in energy conversion and advanced oxidation processes for refractory wastewater treatment.

Mg–CNTs composite prepared by ball milling with PVDF promoted the in situ synthesis of H₂O₂.     

Hydrogen storage in Mg2Ni(Fe)H4 nano particles synthesized from coarse-grained Mg and nano sized Ni(Fe) precursor

In this work, Mg₂Ni(Fe)H₄ was synthesized using precursors of nano Ni(Fe) composite powder prepared through arc plasma method and coarse-grained Mg powder. The microstructure, composition, phase components and the hydrogen storage properties of the Mg–Ni(Fe) composite were carefully investigated. It is observed that the Mg₂Ni(Fe)H₄ particles formed from the Mg–Ni(Fe) composite have a diameter of 100–240 nm and a portion of Fe in the Ni(Fe) nano particles transformed into α-Fe nano particles with the diameter of 40–120 nm. DSC measurements showed that the peak desorption temperature of the Mg₂Ni(Fe)H₄ was reduced to 501 K and the apparent activation energy for hydrogen desorption of the Mg₂Ni(Fe)H₄ was 97.2 kJ mol⁻¹ H₂. The formation enthalpy of Mg₂Ni(Fe)H₄ was measured to be −53.1 kJ mol⁻¹ H₂. The improvements in hydrogen sorption kinetics and thermodynamics can be attributed to the catalytic effect from α-Fe nano particles and the destabilization of Mg₂NiH₄ caused by the partial substitution of Ni by Fe, respectively.

Mg₂Ni(Fe)H₄ was synthesized from precursors of coarse grained Mg powder and Ni(Fe) nano particles with improved hydrogen sorption kinetics and thermodynamics as compared to Mg₂Ni(Fe)H₄.     

Solution combustion synthesis of Ni/La2O3 for dry reforming of methane: tuning the basicity via alkali and alkaline earth metal oxide promoters

The production of syngas via dry reforming of methane (DRM) has drawn tremendous research interest, ascribed to its remarkable economic and environmental impacts. Herein, we report the synthesis of K, Na, Cs, Li, and Mg-promoted Ni/La₂O₃ using solution combustion synthesis (SCS). The properties of the catalysts were determined by N₂ physisorption experiments, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and H₂-TPR (temperature programmed reduction). In addition, their catalytic performance towards DRM was evaluated at 700 °C. The results demonstrated that all catalysts exhibited porous structures with high specific surface area, in particular, Mg-promoted Ni/La₂O₃ (Mg–Ni–La₂O₃) which depicted the highest surface area and highest pore volume (54.2 m² g⁻¹, 0.36 cm³ g⁻¹). Furthermore, Mg–Ni–La₂O₃ exhibited outstanding catalytic performance in terms of activity and chemical stability compared to its counterparts. For instance, at a gas hourly space velocity (GHSV) of 30 000 mL g⁻¹ h⁻¹, it afforded 83.2% methane conversion and 90.8% CO₂ conversion at 700 °C with no detectable carbon deposition over an operating period of 100 h. The superb DRM catalytic performance of Mg–Ni–La₂O₃ was attributed to the high specific surface area/porosity, strong metal-support interaction (MSI), and enhanced basicity, in particular the strong basic sites compared to other promoted catalysts. These factors remarkably enhance the catalytic performance and foster resistance to coke deposition.

Alkali and alkaline earth metal oxides-promoted Ni/La₂O₃ catalysts synthesized by solution combustion synthesis revealed enhanced catalytic performance towards dry reforming of methane.     

Electrochemical investigation and amperometry determination iodate based on ionic liquid/polyoxotungstate/P-doped electrochemically reduced graphene oxide multi-component nanocomposite modified glassy carbon electrode

A novel modified glassy carbon electrode (GCE) was successfully fabricated with a tetra-component nanocomposite consisting of (1,1′-(1,4-butanediyl)dipyridinium) ionic liquid (bdpy), SiW₁₁O₃₉Ni(H₂O) (SiW₁₁Ni) Keggin-type polyoxometalate (POM), and phosphorus-doped electrochemically reduced graphene oxide (P-ERGO) by electrodeposition technique. The (bdpy)SiW₁₁Ni/GO hybrid nanocomposite was synthesized by a one-pot hydrothermal method and characterized by UV-vis absorption, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric-differential thermal analysis (TGA/DTA), and transmission electron microscopy (TEM). The morphology, electrochemical performance, and electrocatalysis activity of the nanocomposite modified glassy carbon electrode ((bdpy)SiW₁₁Ni/P-ERGO/GCE) were analyzed by field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), square wave voltammetry (SWV), and amperometry, respectively. Under the optimum experimental conditions, the as-prepared sensor showed high sensitivity of 28.1 μA mM⁻¹ and good selectivity for iodate (IO₃⁻) reduction, enabling the detection of IO₃⁻ within a linear range of 10–1600 μmol L⁻¹ (R² = 0.9999) with a limit of detection (LOD) of 0.47 nmol L⁻¹ (S/N = 3). The proposed electrochemical sensor exhibited good reproducibility, and repeatability, high stability, and excellent anti-interference ability, as well as analytical performance in mineral water, tap water, and commercial edible iodized salt which might provide a capable platform for the determination of IO₃⁻.

Constructing a sensitive electrochemical sensor based on (bdpy)SiW₁₁Ni/P-ERGO/GCE for IO₃⁻ detection at the nanomolar level with noticeable selectivity.     

Correction: Electrochemical investigation and amperometry determination iodate based on ionic liquid/polyoxotungstate/P-doped electrochemically reduced graphene oxide multi-component nanocomposite modified glassy carbon electrode

Correction for ‘Electrochemical investigation and amperometry determination iodate based on ionic liquid/polyoxotungstate/P-doped electrochemically reduced graphene oxide multi-component nanocomposite modified glassy carbon electrode’ by Minoo Sharifi et al., RSC Adv., 2021, 11, 8993–9007, DOI: 10.1039/D1RA00845E.

The authors regret that eqn (3) and (4) were shown incorrectly in the original article.The corrected equations are shown below.3H₄SiW₄^VW₇^VINi(H₂O)O₃₉⁶⁻ + IO₃⁻ → 3H₂SiW₂^VW₉^VINi(H₂O)O₃₉⁶⁻ + I⁻ + 3H₂O (3)3H₆SiW₆^VW₅^VINi(H₂O)O₃₉⁶⁻ + IO₃⁻ → 3H₄SiW₄^VW₇^VINi(H₂O)O₃₉⁶⁻ + I⁻ + 3H₂O (4)The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

A novel resource utilization method using wet magnesia flue gas desulfurization residue for simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium containing industrial wastewater

In the present study, a novel resource utilization method using wet magnesia flue gas desulfurization (FGD) residue for the simultaneous removal of ammonium nitrogen (NH₄–N) and heavy metal pollutants from vanadium (V) industrial wastewater was proven to be viable and effective. In this process, the wet magnesia FGD residue could not only act as a reductant of hexavalent chromium [Cr(vi)] and pentavalent vanadium [V(v)], but also offered plenty of low cost magnesium ions to remove NH₄–N using struvite crystallization. The optimum experimental conditions for Cr(vi) and V(v) reduction are as follows: the reduction pH = 2.5, the wet magnesia FGD residue dose is 42.5 g L⁻¹, t = 15.0 min. The optimum experimental conditions for NH₄–N and heavy metal pollutants removal are as follows: the precipitate pH = 9.5, the n(Mg²⁺) : n(NH₄⁺) : n(PO₄³⁻) = 0.3 : 1.0 : 1.0, t = 20.0 min. Finally the NH₄–N, V and Cr were separated from the vanadium containing industrial wastewater by forming the difficult to obtain, soluble coprecipitate containing struvite and heavy metal hydroxides. The residual pollutant concentrations in the wastewater were as follows: Cr(vi) was 0.047 mg L⁻¹, total Cr was 0.1 mg L⁻¹, V was 0.14 mg L⁻¹, NH₄–N was 176.2 mg L⁻¹ (removal efficiency was about 94.5%) and phosphorus was 14.7 mg L⁻¹.

A novel resource utilization method using wet magnesia flue gas desulfurization residue for the simultaneous removal of ammonium nitrogen and heavy metal pollutants from vanadium industrial wastewater was proven to be viable and effective.     

Distribution characteristics of nitrogen and the related microbial community in the surface sediments of the Songhua River

Nitrogen in surface sediments is becoming an ecological risk to the river environment and it is essential to clarify the relationship between the different forms of nitrogen and related microorganisms. A survey was conducted to analyze the distribution characteristics of the nitrogen and related microbial community in the sediments of the Songhua River during normal season and dry season. In the surface sediments of the Songhua River, no total nitrogen (TN) pollution risk was observed according to the U.S. EPA assessment criteria (1000 mg kg⁻¹) for sediment contamination, but TN in several sampling sites (554.9–759.7 mg kg⁻¹) exceeded the alert values (550 mg kg⁻¹) should be concerned according to the guidelines issued by the Ministry of Environment and Energy of Ontario, Canada. The average TN, NH₄⁺–N, NO₃⁻–N and total organic nitrogen (TON) in the surface sediments of the Songhua River during normal season were higher than those in the dry period. TON was the main form of nitrogen in the sediment of Songhua River, NO₂⁻–N content was lowest and no obvious difference was observed between normal and dry seasons. The highest average NH₄⁺–N of both seasons occurred in the Nenjiang River, and the highest average NO₃⁻–N of both seasons were found in the main stream of the Songhua River. The community abundance of AOB genes (1.1 × 10⁷ to 2.5 × 10⁸ copies per g soil in normal season, 7.2 × 10⁵ to 3.3 × 10⁸ copies per g soil in dry season) was higher than that (1.2 × 10⁶ to 9.7 × 10⁷ copies per g soil in normal season, 6.6 × 10⁴ to 3.2 × 10⁷ copies per g soil in dry season) of AOA genes in both normal and dry seasons. The denitrifying nirS genes were predominant in both seasons, and their abundance (1.8 × 10⁶ to 8.0 × 10⁸ copies per g soil) in dry season was higher than that (9.7 × 10⁵ to 4.6 × 10⁸ copies per g soil) in normal season. Moreover, the moisture concentration, pH, dissolved oxygen and different formation of nitrogen were key factors affecting the variation of nitrogen-transformation microorganisms during normal and dry seasons. This research could help to explain the relationship between nitrogen transformation and the related microbial community in the surface sediment, which could provide a scientific basis for water ecological restoration and water environment improvement of Songhua River.

In this study, temporal and spatial distribution of nitrogen in the Songhua River sediments and distribution characteristics of related microbes as well as the relationship between them were investigated.     

Solid base catalysts derived from Ca–Al–X (X = F−, Cl− and Br−) layered double hydroxides for methanolysis of propylene carbonate

The Ca–Al and Ca–Al–X (X = F⁻, Cl⁻ and Br⁻) catalysts were prepared via thermal decomposition of Ca–Al layered double hydroxides (LDHs), and tested for methanolysis of propylene carbonate (PC) to produce dimethyl carbonate (DMC). The catalytic performance of these catalysts increased in the order of Ca–Al–Br⁻ < Ca–Al < Ca–Al–Cl⁻ < Ca–Al–F⁻, which was consistent with the strong basicity of these materials. The recyclability test results showed that the addition of Al and halogens (F⁻, Cl⁻ and Br⁻) not only stabilized the CaO but also improved the recyclability of the catalysts. Particularly, the Ca–Al–F⁻ catalyst exerted the highest stability after 10 recycles. These catalysts have an important value for the exploitation of DMC synthesis by transesterification of PC with methanol.

The CA-F⁻ catalyst modified with Al³⁺ and F⁻ was highly active and recyclable for dimethyl carbonate synthesis.     

CO2–C evolution rate in an incubation study with straw input to soil managed by different tillage systems

A laboratory incubation experiment was conducted to assess the impact of straw input on CO₂–C emissions. After the winter wheat (Triticum aestivum L.) growing season, soil samples were collected from the 0–20 cm soil layer. The experiment was conducted on a brown loam soil, classified as a Udoll according to the U. S. soil taxonomy. Treatment levels consisted of three tillage practices: sub-soiling (ST), no-till (NT) and the conventional tillage (CT), two straw management (with and without input of straw), three temperature (25, 30 and 35 °C), and three moisture regimes (55%, 65% and 75% of field moisture capacity or FMC). The results showed that the rate of straw decomposition was the highest in the soil under NT management. The relationship between rate of cumulative CO₂–C and straw decomposition was significant under NT (R² = 0.52). The soil CO₂–C release under incubation was significantly higher with than without the input of straw (R² = 0.95). Furthermore, soil respiration increased with increases in incubation temperature and FMC. At 75% FMC, the rate of CO₂–C release increased by 21.9 mg kg⁻¹ d⁻¹ at 30 °C and 32.0 mg kg⁻¹ d⁻¹ at 35 °C compared with that at 25 °C. At 35 °C, the rate of CO₂–C release increased by 43.6 mg kg⁻¹ d⁻¹ at 65% FMC and 51.2 mg kg⁻¹ d⁻¹ at 75% FMC incubation than that of at 55% FMC under ST. The degree of control on the CO₂–C evolution rate during the pre-incubation period and with higher incubation temperature and FMC was better for the soil from NT than that from CT and ST, and better yet for the soil from ST than that from CT.

A laboratory incubation experiment was conducted to assess the impact of straw input on CO₂–C emissions.     

Partial denitrification coupled with immobilization of anammox in a continuous upflow reactor

Based on the stable operation of a continuous upflow reactor, immobilized anammox coupling with partial denitrification (DEAMOX), was successfully achieved after 94 days operation with a 63.5% accumulation rate of NO₂⁻–N and a 98.4% removal rate of NO₃⁻–N. Moreover, the findings show that the optimum range of COD/NO₃⁻–N ratio for the coupling reaction was 2.3–2.7. The nitrogen removal performance of the coupling reactor decreased in response to the increase of pH value to 8.0 or 8.5, which was inconsistent with previously published results. Complete denitrification was successfully coupled with DEAMOX by adding polycaprolactone (PCL) as solid carbon source. As a result, the NO₃⁻–N produced via anaerobic ammonium oxidation could be completely removed; the removal rate of total nitrogen increased from 80.3% to 88.5%. In addition, a large number of denitrifying biofilms were attached to the surface of PCL particles.

Based a continuous upflow reactor stably operating, immobilized anammox coupling with partial denitrification (DEAMOX), was successfully achieved after 94 days operation with a 63.5% accumulation rate of NO₂⁻–N and a 98.4% removal rate of NO₃⁻–N.     

Rapid iodine capture from radioactive wastewater by green and low-cost biomass waste derived porous silicon–carbon composite

The effective and safe capture and storage of radioactive iodine (¹²⁹I or ¹³¹I) are of significant importance during nuclear waste storage and nuclear energy generation. Herein, a porous silicon–carbon (pSi–C) composite derived from paper mill sludge (PMS) is synthesized and used for rapid iodine capture. The influences of the activator type, the impregnation ratio of the paper mill sludge to the activator, carbonization temperature, and carbonization time on the properties of the pSi–C composite are investigated. The pSi–C composite produced in the presence of ZnCl₂ as the activator and at an impregnation ratio of 1 : 1, a carbonization temperature of 550 °C, and a carbonization time of 90 min has a surface area of 762.13 m² g⁻¹. The as-synthesized pSi–C composite exhibits promising iodine capture performance in terms of superior iodine adsorption capacity (q_t) of around 250 mg g⁻¹ and rapid equilibrium adsorption with in 15 min. The devised method is environmentally friendly and inexpensive and can easily be employed for the large-scale production of porous silicon-activated carbon composites with excellent iodine capture and storage from iodine-contaminated water.

The effective and safe capture and storage of radioactive iodine (¹²⁹I or ¹³¹I) are of significant importance during nuclear waste storage and nuclear energy generation.     

Effect of SiO2 amount on heterogeneous base catalysis of SiO2@Mg–Al layered double hydroxide

The effects of SiO₂ amount on the base catalysis of highly active finely crystallized Mg–Al type layered double hydroxides prepared by the co-precipitation method with coexistence of SiO₂ spheres, denoted as SiO₂@LDHs, were investigated. With the Si/(Mg + Al) atomic ratios of 0–0.50, the highest activity for the Knoevenagel condensation was observed in the case of Si/(Mg + Al) = 0.17, as the reaction rate of 171.1 mmol g(cat)⁻¹ h⁻¹. The base activity increased concomitantly with decreasing LDH crystallite size up to Si/(Mg + Al) atomic ratio of 0.17. However, above the Si/(Mg + Al) atomic ratio of 0.17, the reaction rate and TOF_base were decreased although the total base amount was increased. Results of TEM-EDS and ²⁹Si CP-MAS NMR suggest that the co-existing SiO₂ causes advantages for dispersion and reduction of the LDH crystallite to improve the base catalysis of SiO₂@Mg–Al LDH, whereas the excess SiO₂ species unfortunately poisons the highly active sites on the finely crystallized LDH crystals above a Si/(Mg + Al) atomic ratio of 0.17. According to these results, we inferred that the amount of spherical SiO₂ seeds in the co-precipitation method is an important factor to increase the base catalysis of SiO₂@LDHs; i.e. the control of Si/(Mg + Al) atomic ratio is necessary to avoid the poisoning of highly active base sites on the LDH crystal.

The effects of SiO₂ amount on the base catalysis of highly active finely crystallized Mg–Al LDH(s) prepared by the co-precipitation method with coexistence of SiO₂ sphere seeds were investigated by XRD, ICP, ²⁹Si NMR, TEM-EDS and other techniques.