Presence Of Dicyandiamide Research Articles

(Digital Presentation) In-Situ Growth of CNT and Macroporous ZIF on Bacterial Cellulose for High Frequency Electrochemical Capacitor

High frequency electrochemical capacitors (HF-ECs) represent a class of devices characterized by their high capacitive density and operational capability within the hundreds or kilohertz range. As electronic devices continue to undergo downsizing trends, HF-ECs emerge as promising alternatives to bulky aluminum electrolytic capacitors (AECs), which are constrained by their limited working frequency of approximately 1 Hz and slow charge-discharge rates. The designing of electrodes of HF-ECs combines large surface area for capacitive density along with open porous network to facilitate rapid ion transport. In this study, we synthesized nickel coordinated ZIF-8 (Zeolitic Imidazole Framework-8) cages on bacterial cellulose (BC). The samples underwent rapid carbonization in the presence of dicyandiamide at ~950˚C for 20 minutes, during which the zinc centers inside the MOF cages evaporated forming macroporous structures, while the nickel particles gave rise to carbon nanotube (CNT) growth through tip growth mechanism. The uniform coverage of BC with macroporous ZIF cages reduces the microporous effect, while the CNT growth also imparts higher electronic conductivity via graphitic nitrogen groups. The HF-ECs made with these electrodes and 6M KOH aqueous electrolyte gave a capacitive density of ~3.4 mFcm-2 and a phase angle of -81.3˚. The electrodes were stacked in pairs of 2 and 3 to achieve higher capacitance of 6.3 mFcm-2 and 8.9 mFcm-2 respectively. The HF-ECs were also assembled with 1 M TEABF4 in acetonitrile to show higher working voltage of these electrodes. The device maintained a capacitance just above 3 mFcm-2 and a phase angle over -80˚. The cells show an excellent working capability at higher discharge rates of 100 mAcm-2, where they retained ~70% of the initial capacitance. Figure 1

Valorization of kapok fiber by phosphorylation with a reactive phosphorus‐ and nitrogen‐containing flame retardant for enhanced fire safety

AbstractKapok fiber (KF) with a naturally hollow structure has found an increasing application in filling and composite materials, most of which have a demand of flame retardancy. To realize this high‐value utilization, KF was phosphorylated by a reactive phosphorus‐ and nitrogen‐containing flame retardant for enhanced fire safety. The flame retardant was first synthesized by the reaction of urea and diethylene triamine pentakis (methyl phosphonic acid) (a commercially available scale inhibitor) with low cost, and then, applied in the phosphorylation of KF in the presence of dicyandiamide. In thermogravimetric analysis, phosphorylated KF showed 38.1% residue weight in nitrogen and 10.2% residue weight in air at 700°C, whereas the residue weight of KF was 8.4% in nitrogen and 1.5% in air. In microcalorimetric analysis, the heat release capacity and total heat release of phosphorylated KF displayed a reduction of 81% and 55%, respectively. In vertical combustion test, phosphorylated KF was difficult to ignite and had no afterburning or smoldering. The tests indicated that phosphorylated KF had excellent charring properties, low heat release, and good flame retardancy. This work suggests a promising strategy of enhancing the flame retardancy of KF and increasing its applicability in filling and composite materials.

CO2 Turned into a Nitrogen Doped Carbon Catalyst for the Fuel Cell and Metal-Air Battery Applications

Metal-free catalysts based on nitrogen-doped carbon are among the most promising replacements for Pt-based materials on polymer electrolyte membrane fuel cell (PEMFC) cathodes due to their inherent stability (lack of metal atoms bypasses most of the degradation mechanisms encountered in metal-based non-precious metal catalysts). However, the production of carbon nanostructures that have suitable oxygen reduction reaction (ORR) activities for fuel cell cathode use can create massive amounts of CO2 as a by-product, which counteracts the environmental friendliness of fuel cells. Here, we demonstrate a new method for creating ORR catalysts directly from CO2, which can produce a catalyst with a negative carbon footprint instead of a positive one. Via a fused Li-K carbonate eutectic mixture or pure Li2CO3, CO2 was split into gaseous oxygen and solid carbon, which was then doped with nitrogen using a pyrolysis process with the presence of dicyandiamide and polyvinylpyrrolidone. A thorough physico-chemical characterization of the catalyst materials is presented alongside their electrocatalytic properties for the ORR. The reasons for the properties of the resulting carbon depending on the electrolyte mixture for CO2 electrolysis and deposition temperature are explored. The best performing material had ORR activity nearing that of Pt/C, showing the potential that this method has for creating competitive catalysts while remaining environmentally benign [1]. References Ratso, S.; Walke, P. R.; Mikli, V.; Ločs, J.; Šmits, K.; Vītola, V.; Šutka, A.; Kruusenberg, I. CO2 Turned into a Nitrogen Doped Carbon Catalyst for Fuel Cells and Metal–Air Battery Applications. Green Chem. 2021, 23 (12), 4435–4445. https://doi.org/10.1039/D1GC00659B. Figure 1

Atomic Bridging of Metal‐Nitrogen‐Carbon toward Efficient Integrated Electrocatalysis

AbstractThe rational design of robust electrocatalysts for efficient integrated devices is crucial to enhance energy conversion performance. The coordination of organic ligands with metal ions provides high flexibility to anchor metal atoms among carbon materials. Herein, the atomic anchoring of Zn and Ni atoms into N‐doped carbon networks with adjustable atomic structure is developed by the facile pyrolysis of metal‐organic framework nanoplates in the presence of dicyandiamide. Theoretical calculations reveal the descriptor‐based design principles to adjust the bridging structures of metal‐nitrogen‐carbon moieties with changing d‐band centers, thereby improving electrocatalytic performance. The resulting electrocatalyst displays good multiple electrocatalytic activities for carbon dioxide reduction, oxygen reduction, and evolution reactions, enabling the fabrication of integrated energy devices. Importantly, the CO2‐H2O overall splitting with the as‐prepared electrocatalysts has been driven by the commercial solar cell and the zinc‐air battery assembled with the same catalyst respectively, showing high CO faradaic efficiency up to 90%. Especially, the overall solar‐to‐CO conversion efficiency is up to 13% and the corresponding utilization efficiency of solar‐to‐electricity can reach 54.4%, demonstrating the large promising space to chase the limit that solar cells can possibly achieve. This work provides new opportunities to modulate the atomic bridging structure of metal‐nitrogen‐carbon for integrated electrolysis.

Flower‐like Nitrogen‐co‐doped MoS2@RGO Composites with Excellent Stability for Supercapacitors

AbstractNitrogen‐co‐doped MoS2@rGO composites (named hereafter N‐MoS2@N‐RGO) are prepared by the hydrothermal method using dicyandiamide or hydrazine monohydrate as the nitrogen source. N‐MoS2@rGO is obtained by the hydrothermal reaction of thioacetamide, ammonium molybdate and GO precursors in the presence of dicyandiamide, while N‐MoS2@N‐RGO is synthesized using the same precursors in the presence of hydrazine monohydrate as the nitrogen source. On the one hand, N‐MoS2@RGO displays excellent performance and good capacitance value of 335 F/g acquired at 0.5A/g and improved stability (∼94% of the original capacitance is preserved after 5000 cycles). On the other hand, compared with N‐MoS2@RGO, N‐MoS2@N‐RGO possesses a slightly higher capacitance of 340 F/g recorded at 0.5A/g and better cycling stability (∼98% of its original value after 5000 cycles). Taken together, the results of this investigation clearly indicate that the fabricated composites have application prospect in energy storage devices.

Dual Evolution in Defect and Morphology of Single‐Atom Dispersed Carbon Based Oxygen Electrocatalyst

AbstractThe structure design and atomic modulation of catalysts are two sides of the same coin, both of which are deemed critical factors to regulate the intrinsic electrocatalytic activity. Herein, cobalt single‐atom anchored on nitrogen‐doped graphene‐sheet@tube (CoSAs‐NGST) is derived from a novel Co, Zn‐coordinated zeolitic imidazolate framework (CoZn‐ZIF) in the presence of dicyandiamide. CoSAs‐NGST exhibited a hybrid structure with a bamboo‐like graphene tube and sheet. The atomic configuration of intrinsic defects is characterized by electron energy loss spectroscopy. The morphology differentiation from cake‐shape structure to low‐dimension hybrid not only enhances the dispersity of single atoms but also induces defect state evolution, which results in the formation of a CoN4‐rich graphene tube. Density functional theory (DFT) modeling revealed that the coupling effect on oxygen reduction reaction and oxygen evolution reaction (ORR/OER) pathways of Co‐N4‐tube and Co‐N4‐sheet is responsible for the enhanced activity of CoSAs‐NGST. In addition to the superb ORR/OER bifunctional catalytic performance, CoSAs‐NGST also demonstrates a notably small charge–discharge voltage drop of 0.93 V when applied in the rechargeable zinc–air battery outperforming Pt/C + RuO2 catalyst. The present study provides an insight into the relationship between the structure design and atomic modulation of the carbon based catalysts.

Novel Way to Turn Spent Li-Ion Battery Graphite into Valuable and Active Catalyst for Electrochemical Oxygen Reduction

Employing Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world but, due to the short application time for any given battery (1-3 years) [1], the quantity of spent LIBs (SLIBs) waste is becoming substantial. As LIBs contain different valuable materials (the cathode layer holds Li, Co, Ni, Mn, Al and the anode layer graphite and Cu), the recycling of SLIBs is economically and environmentally beneficial. Additionally, the potential resource strain, as well of the geographical limitations found in the mining/production of the raw materials, will make recycling crucial for sustainable production of LIBs. However, current SLIBs recycling strategies has been focused on cathode materials alone while largely overlooking the anode of the battery [1–3]. In turn, anode recycling has so far concentrated mostly on the metal in the electrode and only very recently has the focus shifted towards the recycling of graphite powders.In this work, a novel strategy for recycling SLIB graphite and reforming it as a valuable catalyst material for electrochemical oxygen reduction reaction (ORR) is proposed. A modified Hummers method was used to fabricate graphene oxide (GO) from SLIB graphite powder. The GO doping was done by pyrolyzing at 800 °C in the presence of dicyandiamide (DCDA). The mass ratio of GO-to-DCDA was 1:20. The prepared nitrogen-doped graphene, from SLIB graphite powder, (NG-Bat) was characterised by various physical (XRD, Raman, XPS, SEM, TEM) and electrochemical characterization methods. Electrochemical properties of the catalyst material was investigated by using the rotation disc electrode voltammetry and electrochemical impedance methods. For electrochemical characterisation the glassy carbon (CG) electrodes were modified with synthesized catalyst and the experiments were carried out in 0.1 M KOH solution. The GC disc electrodes were modified with NG ethanol suspensions (4 mgcatalyst ml-1) containing 6 µl aQAPS-S14 (2%) ionomer from Hephas Energy per 1ml ethanol. The physical and electrochemical characteristics of NG-Bat were compared with commercially available nitrogen doped graphene (NG-Com).Based on XRD and Raman data, it was shown that SLIB-derived graphite maintains its high quality, even after intense exploitation in the batteries and is therefore a valuable material that is worth recycling. The homogeneous distribution of carbon, nitrogen, and oxygen in NG-Bat was demonstrated by elemental mapping. The overall nitrogen content in NG-Bat was found to be 18.4 at%, from which pyridinic N constitutes 55.5 at%, graphitic N 21.7 at%, pyrrolic N 17.8 at% and oxidized N 5.0 at%. The onset potential of the ORR for the NG-Bat catalyst material is −0.11 V, and for the NG-Com catalyst −0.18V (Figure 1). The NG-Bat shows a larger oxygen reduction current and higher electrocatalytic activity than the catalyst based on NG-Com. Based on EIS fitting results very different charge transfer resistance and double-layer capacitance values are achived, probably caused by different conductivities of the catalyst materials. Catalyst material NG-Bat showed much high electrocatalytic activity towards the ORR than did a NG-Com, caused probably by a higher content of active nitrogen species and the presence of carbon vacancies on the surface of graphene, as confirmed by XRD, Raman and XPS experiments.These findings demonstrate that SLIB graphite is still a valuable material and a very suitable precursor for GO fabrication and SLIB anode layer needs to be recycled and returned to usage in a new form. Based on the result of this work, one of the potential applications of the SLIB-derived graphene could be the production of catalyst material for the oxygen reduction reaction (ORR), thereby open new avenues to the fuel cell, metal-air battery, and sensor industries.

Effects of dicyandiamide on cadmium accumulation in pakchoi under instant soluble nitrogen fertilizers

We investigated the effects of dicyandiamide (DCD) on the growth and Cd concentrations in pakchoi cultivated under different instant soluble N fertilizers [ammonium sulfate, ammonium sulfate and sodium nitrate (1:1, ammonium/nitrate), and urea] in Cd-contaminated soils. The results showed that the fresh weight of the edible parts of Cd-stressed pakchoi were increased by 583.3%, 41.5%, and 206.8% under ammonium, ammonium/nitrate, and urea treatments in the presence of DCD, respectively compared with control, and the tolerance index and photosynthetic rate significantly increased, whereas no significant changes were observed under nitrate supply. Under all N treatments with DCD, the MDA and H2O2 contents and the superoxide radical production rate in the leaves of pakchoi were decreased, with the highest reduction occurred in ammonium and urea treatments. Cd concentrations in the leaves of pakchoi fertilized with ammonium, ammonium/nitrate, and urea were lowered by 58.3%, 34.0%, and 44.5% and those in the petioles were lowered by 61.8%, 29.4%, and 55.6%, respectively. Cd concentration in the leaves and petioles of pakchoi in the nitrate treatment did not differ significantly from control. These changes could be attributable to the reduction in the acidification of rhizosphere soil in response to the combined application of N fertilizer and DCD. Accordingly, in Cd-contaminated soils with a low buffering capacity, the application of DCD combined with ammonium, ammonium/nitrate, or urea N fertili-zers could alleviate Cd-induced growth stress and inhibit photosynthesis in pakchoi plants and effectively minimize the Cd accumulation.

New fire-resistant epoxy thermosets: nonisothermal kinetic study and flammability behavior

Abstract New fire-resistant thermosets are prepared based on a bisphenol A-epoxy resin which is thermally crosslinked in the presence of dicyandiamide and two phenols containing phosphorus atoms. The thermosets are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis (TGA), and microscale combustion calorimetry (MCC) tests. A nonisothermal kinetic study is performed based on processing of TGA data applying the method proposed by Vyazovkin. The lifetime prediction analyses establish that the phosphorus-containing polymers could be used at a constant temperature of 200°C up to 200–780 min. The MCC tests reveal an improvement of the flammability behavior, as well as a significant heat release capacity reduction for phosphorus-containing samples compared to the sample which has no phosphorus component.

Nitrogen-doped carbon-based electrocatalysts synthesised by ball-milling

Herein, for the first time, ball-milling of carbon materials (e.g. graphite, graphene oxide or graphene) in the presence of dicyandiamide (DCDA) followed by heat treatment at 800 °C was employed to synthesise N-doped carbons for the oxygen reduction reaction (ORR) in alkaline medium. The obtained results highlight that: i) the N-doped nanocarbon catalysts synthesis process employed herein is easy and could be used without hazardous solvents; ii) X-ray photoelectron spectroscopy indicated successful N-doping, iii) N-doped graphite and graphene are Mn-free as confirmed by the ICP-MS analysis, iv) the ORR electrocatalytic activity depends on the carbon source used for the catalyst preparation and v) all the N-doped nanocarbons revealed better ORR performance than the undoped materials.

Transition metal-nitrogen co-doped carbide-derived carbon catalysts for oxygen reduction reaction in alkaline direct methanol fuel cell

In this work, we demonstrate the electrocatalytic properties of cobalt- and iron-containing nitrogen-doped carbide-derived carbon materials in the oxygen reduction reaction (ORR) and utilise these as cathode catalysts in an alkaline direct methanol fuel cell. The carbide-derived carbon material is produced by chlorination of titanium carbide, which is then pyrolysed in the presence of dicyandiamide and either a cobalt or iron salt. The electrocatalytic activity towards the ORR and stability of the catalyst materials is tested in 0.1M KOH solution employing the rotating disk electrode (RDE) method and compared to a commercial Pt/C catalyst. The elemental composition in the bulk of the materials is studied using energy dispersive X-ray spectroscopy and on the surface by X-ray photoelectron spectroscopy. Scanning electron microscopy is used to investigate the surface morphology of the resulting catalysts. The performance of the catalysts is also compared in alkaline direct methanol fuel cell. The catalysts’ performance is comparable to that of Pt/C in both RDE and fuel cell measurements and rather peculiar morphologies are observed by the growth of carbon nanotubes during pyrolysis. Overall, these novel catalysts show great potential for application in alkaline direct methanol fuel cells.

Amelioration of an acidic ultisol by straw-derived biochars combined with dicyandiamide under application of urea.

The rapid increase in agricultural pollution demands judicious use of inputs and outputs for sustainable crop production. Crop straws were pyrolyzed under oxygen-limited conditions at 400°C for 2h to prepare peanut straw biochar (PB), canola straw biochar (CB), and wheat straw biochar (WB). Then, 300-g soils were incubated each with urea nitrogen (UN) and UN + biochars with or without dicyandiamide (DCD) for 60days. During the incubations, soil acidification induced by urea was somewhat inhibited by biochars, but nitrification of hydrolyzed NH4+ produced much more acidity than the neutralization potential of the biochars. In single UN (200mg/kg) treatment, soil pH decreased drastically and the final pH after incubation was lower than the control. Antagonistic to UN, all three biochars neutralized the soil acidity, which was consistent to their inherent alkalinity. DCD inhibited nitrification which was obvious throughout the incubations, as 30mg/kg DCD+200mg/kg UN combined with 1% PB, CB, and WB retained 0.94, 0.79, and 1.19units higher pH, respectively, and significantly reduced exchangeable acidity over the treatments without DCD (P<0.05). The treatments of UN + biochars with and without DCD had highly significant effects on soil pH, exchangeable Al3+, NH4+-N, (NO3-+NO2-)-N, and available P (P<0.05). Amplified NH4+-N retentions at higher rates of PB referred increased negatively charged sites for nutrient adsorptions. Applied UN transformations varied among different treatments, and the maximum amounts of total mineral N recovered were 218.3, 218.5, and 223.8mg/kg in the presence of DCD by PB, CB, and WB, compared to 198.2, 201.6, and 205.2mg/kg, respectively, in no DCD treatments. Urea induced severe soil acidification and even lowered the ameliorative effects of applied biochars. Thus, ammonium-based fertilizers must include nitrification inhibitor (DCD) and, if used in combination with biochars will offer a suitable choice to reduce the acidity, improve base saturation and fertility of soil for sustainable agriculture.

Colorimetric and visual determination of dicyandiamide using gallic acid-capped gold nanoparticles

A new method is presented for the visual detection of dicyandiamide (DCD). Gold nanoparticles (AuNPs) capped with gallic acid (GA) were synthesized in a single step at room temperature, using GA as both the reducing agent and stabilizer. In the presence of DCD, the hydrogen-bonding interaction between GA and DCD induces the aggregation of AuNPs, associated with a color change from red to gray that can be observed with bare eye. DCD could be quantified by photometry as the red shift of the maximal absorption band is linearly related to the logarithm of concentration of DCD in the 0.1 to 500 μM concentration range, with a regression coefficient of 0.9987 and a 80 nM detection limit (at an SNR of 3). The proposed method was successfully applied to the detection of DCD in spiked dairy samples.

Palladium Nanoparticles Supported on Nitrogen-Doped Graphene Nanosheets as a Highly Active Electrocatalyst for Oxygen Reduction Reaction

In this study, the oxygen reduction reaction (ORR) on Pd nanoparticle-decorated nitrogen-doped graphene (Pd/NG) catalyst has been investigated in acid and alkaline solutions using the rotating disk electrode (RDE) method.1 Nanoparticles of palladium supported on high surface area carbon have been explored as electrodes for PEMFCs. Pd is a promising alternative to the costly Pt for fuel cell applications. Due to its large surface area and the high electrical conductivity graphene is being used more frequently for electrochemical applications.2 Graphene exhibits several advantages over carbon nanotubes, such as lower cost, larger surface area and more simple preparation. Very important advantage is that graphene synthesized from graphite powder does not contain metallic impurities, which can alter electrochemical properties of carbon nanotubes. Doping graphene with nitrogen atoms is known to result in tunable chemical and physical properties, for example, N-doping improves electrical conductivity of materials, accelerates the growth of nanoparticles on graphene substrate and enhances the catalytic activity of composite materials. It was found recently, that single Pd atoms embedded into N-doped graphene are promising candidates for use in fuel cell cathodes for ORR.3 N-doped graphene was synthesized by pyrolysis of graphite oxide in the presence of dicyandiamide as nitrogen precursor.4NG was further modified with Pd nanoparticles (PdNPs) prepared by borohydride reduction.Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were utilized to study the size and distribution of Pd nanoparticles on substrate surface and the type of nitrogen groups present in the N-doped graphene nanosheets. TEM indicated a good dispersion of Pd nanoparticles on the substrate surface and the average size of the PdNPs was 2.6±0.7 nm (Fig. 1a). The XPS survey spectra showed O1, N1s, C1s and Pd3d peaks for Pd/NG sample (Fig. 1b). Four different types of nitrogen species can be seen in inset N1s spectra. Namely, pyridinic-N at binding energy of 397.8 eV prevails on the surface, peak shoulder between 399 and 400 eV corresponds to pyrrolic-N and graphitic-N and smaller peak at ca. 402.5 eV is due to the presence of pyridine-N-oxide functionalities on the surface.1 The RDE results showed remarkable electrocatalytic activity of Pd/NG catalysts towards the ORR. The prepared Pd/NG materials catalyse a 4-electron reduction of oxygen. At low overpotentials the Tafel slope for oxygen reduction is close to −60 mV dec−1 and at higher current densities the slope is approximately −120 mV dec−1.The Pd/NG composite showed excellent ORR performance in alkaline media (Fig. 2) and is a promising material to be used as a cathode catalyst for alkaline membrane fuel cells.This work not only offers a low-cost and high performance alternative for Pt/C catalysts in fuel cells, but also opens the door towards fabrication of varying types of metal cluster/graphene hybrids that will have wide application in electrocatalysis and clean energy fields.

Rapid determination of trace dicyandiamide in mussels from Zhejiang coast by ultra-fast liquid chromatography-tandem mass spectrometry with isotope internal standard dilution technique.

In this study, a rapid and accurate ultra-fast liquid chromatography-tandem quadrupole mass spectrometry (UFLC-MS/MS) method coupled with the isotope internal standard dilution technique was established and validated to determine trace dicyandiamide (DCD) in mussels. The sample was extracted by acetonitrile, and chromatographic separations were performed on an Acquity UPLC BEH Amide column by using water-acetonitrile (9:91, v/v) as the mobile phase within 3 min. DCD was determined by using DCD-(15)N4 as an internal standard. The results showed that the recoveries were between 96.2 and 103 % with relative standard deviations (RSDs) in the range of 0.6-6.0 %. The limit of quantification (LOQ) was 0.05 μg/kg. This method can be applied to the routine analysis for the rapid and sensitive determination of trace DCD in mussels. Overall, the data reiterate the importance of investigating the presence of DCD in marine biological samples, which can act as food quality controls for human health.

Effects of the nitrification inhibitor dicyandiamide (DCD) on gross N transformation rates and mitigating N2O emission in paddy soils

The nitrification inhibitor dicyandiamide (DCD, C2H4N4) is effective in suppressing nitrification and N2O emission in many agro-ecosystems. However, whether DCD affects other nitrogen (N) transformation processes, and the mechanisms of its inhibitory effects on N2O emission, are not fully understood. In the present study, we conducted a 15N dilution incubation experiment to investigate the effects of DCD on gross N transformation rates and N2O emissions in two paddy soils under an intensive irrigated rice-upland crop rotation system. The duration of microbial inhibition by DCD was also evaluated. We used the numerical model FLUAZ, based on the 15N tracing technique, to calculate gross N transformation rates. The results showed that DCD could effectively inhibit gross N nitrification in the tested soils; however, no influence on N mineralization and immobilization was detected. Lower N2O emissions from both soils were observed in the presence of DCD, due to the dual functions of DCD on both nitrification rates and the fraction of N2O in nitrification products. While, further study to confirm our results by direct measurement of DCD in reducing the fraction of N2O in nitrification products should be conducted. The inhibitory effect of DCD on gross N nitrification and N2O emission decreased over time, and was not statistically significant four weeks after the addition of this inhibitor to the soils.

A New Material Based on Renewable Resources: Chitin and Betaine

Water-insoluble chitin betainate was environmentally friendly prepared by esterifying chitin with betaine hydrochloride in the presence of dicyandiamide by dry process. The process achieved free-pollution and easy treatment. The chitin betainate holds potential as an adsorbent by the results of the adsorption experiments.

Mineral nitrogen in a rhizosphere soil and in standing water during rice (Oryza sativa L.) growth: effect of hydroquinone and dicyandiamide

Inhibitors are applied to improve the efficiency of N fertilizer use and to reduce N losses from the soil. However, little information is available on the effects of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD), on urea-derived mineral N in the rhizosphere of rice plants and in the standing water. Furthermore, this is important to understand the contribution of rice plants to gaseous N losses in the presence of inhibitor(s). A rhizobox was used to simultaneously study urea-derived mineral N in the soil at increasing distances from rice roots, and the effect of growing plants on the behavior of fertilizer-N in soil. The combined application of urea (U) with DCD showed a significantly positive effect on rice growth. The redox potentials in the rhizosphere soil were higher in the presence than in the absence of DCD, especially when rice plants entered their vigorous growth stage. During the entire experimental period, NH 4 + –N concentrations in the rhizosphere of rice plants were smaller in the U + DCD and U + HQ + DCD treatments than in the U and U + HQ treatments. On days 20 and 60 after fertilization, the U + DCD and U + HQ + DCD treatments showed a smaller concentration of (NO 3 − + NO 2 − )–N in soil less than 0.5 cm from the rhizobox, compared to the U treatment. During the early period of rice growth, the NH 4 + –N concentration of the standing water was higher in the presence than in the absence of DCD. However, there were no significant differences in NH 4 + –N among all treatments after 20 days. In the absence of rice plants, also, the application of DCD and especially DCD and HQ, always increased the level of NH 4 + –N and pH in the standing water. Thus, rice plants might reduce potential gaseous N losses from a urea-fertilized, flooded soil, due to the stimulating effect on rice growth in the presence of DCD or DCD + HQ. The N 2 O emissions from the urea-fertilized, rice-planted soil significantly decreased when DCD or DCD + HQ was used. From the results obtained, we conclude that DCD and DCD + HQ together with U can be an effective tool to improving crop growth and reducing N loss as N 2 O in rice cultivation, and that the use of a rhizobox is useful to study the interaction between plant uptake and the behavior of fertilizer-N in soil.

Influence of urease and nitrification inhibitors on N losses from soils fertilized with urea

The aim of this study was to evaluate how the N losses through volatilization and leaching from soils fertilized with urea can be affected by the application of a urease inhibitor or a urease plus a nitrification inhibitor. The experiment was carried out using lysimeters with 15N-labelled urea and N-(n-butyl) thiophosphoric triamide (NBPT) as urease inhibitor and dicyandiamide (DCD) as nitrification inhibitor, comparing three different treatments: urea alone (U), urea + NBPT (UN) and urea + NBPT + DCD (UND). Both volatilization and leaching were significantly different in the soils used, according to their physico-chemical characteristics. However, the pattern of the loss was similar: the volatilization was significantly reduced by NBPT (UN), but the presence of DCD (UND) significantly increased the loss, with respect to UN. Considering leaching, the highest amount of NO3 – was lost with UND, the lowest with U. The greatest amount of N lost by leaching was soil-derived N produced by the N mineralization-immobilization turnover. We suggest that, by maintaining the NH4 + in the soils, the inhibitors, in particular DCD, caused a priming effect with a subsequent increase in the rate of soil organic matter mineralization and an extra release of soil organic N. The priming effect was real in the sandy loam (SL) soil where a net N release was observed, whereas in the clay loam (CL) soil the effect of the inhibitors was less pronounced and an apparent priming effect was observed; however, a real priming effect also cannot be excluded in this soil.

Nitrification and denitrification in an acidic soil of tea (Camellia sinensis L.) field estimated by δ15N values of leached nitrogen from the soil columns treated with ammonium nitrate in the presence or absence of a nitrification inhibitor and with slow-release fertilizers

Nitrification and denitrification processes of inorganic nitrogen (N) from several fertilizers placed in an acid soil (pH 4.1) of tea fields were examined in two experiments based on the NO3-N leaching pattern from soil columns (20 cm depth) and on the δ15N values of leached N. In the first experiment, ammonium nitrate (AN) was placed in the soil columns with and without dicyandiamide (DCD), a nitrification inhibitor. The NO3-N content in the leachate was more than 10 times higher than the NH4-N content and DCD application decreased the NO3-N content in the leachate. The δ15N values of the leached N with and without DCD initially decreased, with minimum values of − 3.8‰and − 1.5\\%, respectively, which were lower than that of applied AN (+ 0.7\\%). These results showed that 15N depletion occurred by the conversion of NH4-N to NO3-N through nitrification under acidic soil conditions (pH 4.1) and larger isotopic fractionation in the presence of DCD. In the second experiment, four slow-release fertilizers, isobutyriden diurea (IB), oxamide (Oxa), polyolefin-coated area (100-d type; PCU), and rape seed meal (RSM), were placed in the soil columns and changes in the inorganic N content in the leachates were compared with the non-fertilized treatment. At the end of the experiment, the amounts of leached N were 52% and 44% in the treatment with Oxa and RSM, respectively, suggesting that organic N was strongly mineralized under the acidic soil conditions in the tea field. The δ15N values of the leached N from the applied N were calculated from the isotopic balance as compared with the volumes of soil-derived N, which were asuumed to be the same in the presence or absence of fertilization. The cumulative δ15N values of the leached N and of inorganic N remaining in soil suggested that some immobilization of fertilizer N had occurred in the treatment with PCU. The cumulative δ15N values in the treatments with IB, Oxa, and RSM suggested the presence of high rates of denitrification, probably associated with the emission of nitrous oxide commonly observed in tea fields amended with organic materials like rape seed meal.