One-step synthesis of green emission carbon dots for selective and sensitive detection of nitrite ions and cellular imaging application

In recent years, carbon dot (CD)-based fluorescent sensors for selective ions or small biomolecules have drawn great attention. In this work, highly fluorescent CDs (QY = 21%) were prepared from 2,3-diamino pyridine as the precursor through a facile solvothermal process. The CDs showed high stability and a green emission in aqueous, and the optimal emission wavelength of CDs is 508 nm under the excitation wavelength of 438 nm. Interestingly, a CDs-based nanoprobe was developed for a selective and sensitive fluorescence quenching response to NO₂⁻ in water, and the quenching mechanism was investigated in the work. Besides, the recovery rates of NO₂⁻ in the range of 98–103.5% were found to be acceptable, indicating that the proposed CDs could be act as potential candidates for determination of nitrite ions in real samples. Meanwhile, the nanoprobe was also successfully employed in a visualization biosensing platform for determination of NO₂⁻ in living cells due to its eminent biocompatibility.

Schematic route of the carbon dots and their applications for the nitrite detection.     

Wild jujube-based fluorescent carbon dots for highly sensitive determination of oxalic acid

Fluorescent carbon dots (CDs) were synthesized by a one-step hydrothermal treatment of wild jujube and dl-tryptophan. The structure and properties of the CDs were confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible absorption spectroscopy, fluorescence spectroscopy and so on. The as-prepared CDs exhibit excellent excitation-independent but pH-dependent (4.0–12.0) fluorescent features and emit blue strong fluorescence under 365 nm light. Hg²⁺ can decrease the fluorescence intensity of the CDs through static quenching, while the addition of oxalic acid (OA) recovers it owing to the coordination binding between oxalic acid and Hg²⁺. Based on this, the as-prepared CDs were used as a new “off–on” fluorescent probe for highly sensitive determination of oxalic acid with a wide linear detection range of 0.1–20 mg L⁻¹ and a low detection limit of 0.057 mg L⁻¹. Moreover, the fluorescent probe was successfully applied to detect oxalic acid in tomato and cherry tomato samples with satisfactory results.

Carbon dots synthesized from wild jujube and dl-tryptophan can serve as sensitive off–on fluorescent sensors for the detection of oxalic acid.     

Ratiometric fluorescent sensors for nitrite detection in the environment based on carbon dot/Rhodamine B systems

A novel carbon dot/Rhodamine B-based ratiometric fluorescent probe was developed for a highly sensitivity and selective detection of nitrite (NO₂⁻). The probe showed colour changes from blue to orange under ultraviolet light in response to NO₂⁻ with a detection limit as low as 67 nM in the range of 0 to 40 μM. A ratiometric fluorescent test paper was successfully prepared using the probe solution, which demonstrated its feasibility towards a rapid and semi-quantitative detection of NO₂⁻ in real samples.

A visual ratiometric fluorescent sensor based on blue carbon dot/Rhodamine B is used to selectively detect NO₂⁻ in the environment.     

Carbon quantum dots as a fluorophore for “inner filter effect” detection of metronidazole in pharmaceutical preparations

With houttuynia cordata as carbon source, photoluminescent carbon quantum dots (CDs) were obtained via a one-step hydrothermal procedure. The absorption band of metronidazole (MNZ, maximum absorption wavelength at 319 nm) can well overlap with the excitation bands of CDs (maximum excitation wavelength at 320 nm). A fluorescent approach has been developed for detection of MNZ based on the inner filter effect (IFE), in which as-prepared CDs act as an IFE fluorophore and the MNZ as an IFE absorber. We have investigated the mechanism of quenching the fluorescence of CDs and found that the IFE leads to an exponential decay in fluorescence intensity of CDs with increasing concentration of MNZ, but showed a good linear relationship (R² = 0.9930) between ln(F₀/F) with the concentration of MNZ in the range of 3.3 × 10⁻⁶ to 2.4 × 10⁻⁴ mol L⁻¹. Due to the absence of surface modification of the CDs or establishing any covalent linking between the absorber (MNZ) and the fluorophore (CDs), the developed method is simple, rapid, low-cost and less time-consuming. Meanwhile, it possesses a higher sensitivity, wider linear range, and satisfactory selectivity and has potential application for detection of MNZ in pharmaceutical preparations.

CDs were prepared using Houttuynia cordata via hydrothermal process, the absorption band of MNZ can well overlap the excitation bands of CDs, a simple, rapid approach for detection of MNZ was established on the basis of IFE.     

A dual-emission nano-rod MOF equipped with carbon dots for visual detection of doxycycline and sensitive sensing of MnO4−

Herein, ethanediamine-modified carbon dots (CDs) were encapsulated into luminescent MOF(Eu), which was designed for a dual-emission hybrid material (CDs@MOF(Eu)) with diverse fluorescence applications. This material exhibited high selectivity and sensitivity towards doxycycline. With an increasing concentration of doxycycline, the blue light emission of CDs could be quenched, whereas the red light emission of MOF(Eu) was enhanced. In view of this result, more convenient “test paper” was used first as a new tool for doxycycline detection, the colour of which turned from blue-purple to red as observed by the naked eyes under 365 nm UV-irradiation. This hybrid material also was a probe for sensing MnO₄⁻ with a low limit of detection and good anti-interference performance. We propose that CDs can improve detection sensitivity compared with the original MOF(Eu). The possible sensing mechanism was discussed in detail. Importantly, the feasibility of this composite for sensing doxycycline in a simulated biological system and sensing MnO₄⁻ in tap water was investigated.

A dual-emission hybrid material could detect doxycycline and MnO₄⁻ sensitively. Test paper was regarded initially as a tool for doxycycline visual detection. A lower LOD of MnO₄⁻ showed that carbon dots can accelerate quenching speed of MOF(Eu).     

Novel fluorescence sensor for the selective recognition of tetracycline based on molecularly imprinted polymer-capped N-doped carbon dots

A novel fluorescent probe based on molecularly imprinted polymers (MIPs) coupled with N-doped carbon dots (CDs) was prepared and used for specific recognition and sensitive determination of tetracycline (TC). N-doped CDs were synthesized using citric acid as a carbon source and ethylenediamine as a nitrogen source by a microwave assisted pyrolysis method. The determination conditions such as the solvents, material amount, pH value, and temperature were optimized. The CDs-MIPs have the best quenching on TC in water. The proposed method used for TC determination in milk powder samples had a detection limit of 0.054 μg mL⁻¹ and a wide range of 0.5–30 μg mL⁻¹. Meanwhile, satisfactory recoveries were obtained ranging from 95 to 108%. Oxytetracycline, chlorotetracycline and most of the coexisting substances showed no obvious interference indicating that the CDs-MIP probe exhibited high selectivity due to the presence of imprinted sites. Charge transfer from CDs-MIPs to TC may be through the mechanism of fluorescence quenching. This work gives a feasible strategy for the synthesis of N-doped carbon dot based molecularly imprinted polymers used as a fluorescent sensor in the food analysis field.

A novel fluorescent probe based on MIP coupled with N-doped CDs was prepared and used for sensitive recognition of tetracycline.     

Reed-derived fluorescent carbon dots as highly selective probes for detecting Fe3+ and excellent cell-imaging agents

A kind of highly selective and sensitive fluorescent probe for detecting Fe³⁺, carbon dots (CDs), was prepared with renewable reed naturally containing C, N, O, and S elements as a green and eco-friendly carbon source by a simple hydrothermal process. The fluorescence of CDs without purification and surface modification can be quenched by Fe³⁺ in a wide concentration range of 0 to 362 μmol L⁻¹ (concentration of Fe³⁺), with detection limits as low as 0.014 μmol L⁻¹ in 0–50 μmol L⁻¹. Characterizations, such as TEM, XPS, Raman and FTIR, confirmed that the static quenching mechanism involved the generation of non-luminescent complexes between Fe³⁺ and functional groups (carboxyl group, sulfur-oxyl group and hydroxyl group) on the surface of CDs and with the aggregation of CDs. More importantly, CDs had good biocompatibility and nontoxicity according to an MTT cell-viability assay, and cells labeled with CDs emitted blue, green and red color fluorescence. Thus, the static quenching mechanism was confirmed. So, this reed-derived natural CD solution can be utilized in detecting Fe³⁺, culture cells, and cell imaging.

A highly selective and sensitive fluorescent probe for detecting Fe³⁺, carbon dots (CDs), was prepared with renewable reed naturally containing C, N, O, and S elements as a green and eco-friendly carbon source by a simple hydrothermal process.     

Theoretical study of the oxidation reactions of sulfurous acid/sulfite with ozone to produce sulfuric acid/sulfate with atmospheric implications

Herein, theoretical studies were performed on the atmospheric oxidation of sulfurous acid (H₂SO₃) and sulfite ions (HSO₃⁻) by ozone (O₃) to produce sulfuric acid and hydrosulfate ions. The most favorable path for the H₂SO₃ + O₃ reaction has been found to be initiated from concerted H-abstraction and oxygen addition, with an overall energy barrier of 18.3 kcal mol⁻¹. On the other hand, the most favorable path for the HSO₃⁻ + O₃ reaction is initiated from oxygen addition, with an overall energy barrier of only 0.3 kcal mol⁻¹. Kinetic simulations were performed to estimate the significance of these reactions in the formation of atmospheric sulfate and destruction of the ozone layer. The results provide new insight into the missing source of atmospheric sulfate and particulate matter.

Herein, theoretical studies were performed on the atmospheric oxidation of sulfurous acid (H₂SO₃) and sulfite ions (HSO₃⁻) by ozone (O₃) to produce sulfuric acid and hydrosulfate ions.     

Microwave assisted synthesis of negative-charge carbon dots with potential antibacterial activity against multi-drug resistant bacteria

In this research, negative-charge carbon dots (CDs) were synthesized in one-step using a microwave and found to have potential antibacterial ability against multi-drug resistant bacteria. The CDs were synthesized by using citric acid and urea as precursors, and characterized by FT-IR, TEM and fluorescence spectrophotometry. The average size of CDs was about 2.5 nm, and the ζ potential was −11.06 mV. In the following antibacterial activity test, time-killing curve experiments and colony-forming assay were carried out to determine the minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) of the CDs against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate Staphylococcus aureus (VISA). The data showed the MBC of the CDs against MRSA is 2.5 mg mL⁻¹, and the MIC of the CDs against MRSA is 0.63 mg mL⁻¹; the MBC of the CDs against VISA is 1.25 mg mL⁻¹, and the MIC of the CDs against VISA is 0.63 mg mL⁻¹. The results demonstrated that the negative-charge CDs have potential against multi-drug resistant Staphylococcus aureus (S. aureus), and may serve as alternatives for therapy in the future.

In this research, negative-charge carbon dots (CDs) were synthesized in one-step using a microwave and found to have potential antibacterial ability against multi-drug resistant bacteria.     

Reversible ammonia uptake at room temperature in a robust and tunable metal–organic framework

Ammonia is useful for the production of fertilizers and chemicals for modern technology, but its high toxicity and corrosiveness are harmful to the environment and human health. Here, we report the recyclable and tunable ammonia adsorption using a robust imidazolium-based MOF (JCM-1) that uptakes 5.7 mmol g⁻¹ of NH₃ at 298 K reversibly without structural deformation. Furthermore, a simple substitution of NO₃⁻ with Cl⁻ in a post-synthetic manner leads to an increase in the NH₃ uptake capacity of JCM-1(Cl⁻) up to 7.2 mmol g⁻¹.

Recyclable and tunable ammonia adsorption with JCM-1 and JCM-1(Cl⁻) at room temperature occurs reversibly without structural decomposition.     

Shock response of condensed-phase RDX: molecular dynamics simulations in conjunction with the MSST method

We have performed molecular dynamics simulations in conjunction with the multiscale shock technique (MSST) to study the initial chemical processes of condensed-phase RDX under various shock velocities (8 km s⁻¹, 10 km s⁻¹ and 11 km s⁻¹). A self-consistent charge density functional tight-binding (SCC-DFTB) method was used. We find that the N–NO₂ bond dissociation is the primary pathway for RDX with the NO₂ groups facing (group 1) the shock, whereas the C–N bond scission is the dominant primary channel for RDX with the NO₂ groups facing away from (group 2) the shock. In addition, our results present that the NO₂ groups facing away from the shock are rather inert to shock loading. Moreover, the reaction pathways of a single RDX molecule under the 11 km s⁻¹ shock velocity have been mapped out in detail, NO₂, NO, N₂O, CO and N₂ were the main products.

We have performed molecular dynamics simulations in conjunction with the multiscale shock technique (MSST) to study the initial chemical processes of condensed-phase RDX under various shock velocities (8 km s⁻¹, 10 km s⁻¹ and 11 km s⁻¹).     

Poly(quercetin)-bismuth nanowires as a new modifier for simultaneous voltammetric determination of dihydroxybenzene isomers and nitrite

Dihydroxybenzene isomers and nitrite, NO₂⁻, are present in the environment as highly toxic compounds and cause human cancer. In this study, for the first time poly(quercetin) (PQ) was synthesized from the reaction between quercetin (Q) and hydroquinone (HQ) as a linker. Bismuth nanowires (BNWs) were synthesized using a solvothermal technique and then the BNWs and PQ were used for preparation of a novel modified graphite paste electrode (GPE/PQ–BNWs) for simultaneous determination of dihydroxybenzene isomers; HQ, catechol (CC), resorcinol (RS) in the presence of NO₂⁻. The product was characterized using X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The electrochemical response characteristics of the modified GPE toward mix HQ, CC, RS and NO₂⁻ were investigated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under the optimum conditions, detection limits of 0.12, 0.2, 0.82 and 4.5 μM were obtained for HQ, CC, RS and NO₂⁻, respectively. Moreover, the GPE/PQ–BNWs were applied to determine HQ, CC, RS and NO₂⁻ in water samples with satisfactory results.

Dihydroxybenzene isomers and nitrite, NO₂⁻, are present in environment as the high toxic compounds and cause human cancer. A novel GPE/PQ–BNWs for simultaneous determination dihydroxybenzene isomers; HQ, CC, RS in presence of NO₂⁻.     

Impact of the acidic group on the hydrolysis of 2-dinitromethylene-5,5-dinitropyrimidine-4,6-dione

The hydrolysis mechanism and the kinetics of using 2-dinitromethylene-5,5-dinitropyrimidine-4,6-dione (NMP) to prepare the representative insensitive energetic material 1,1-diamino-2,2-dinitroethylene (FOX-7) in a nitric–sulfuric acid system are systematically investigated via a density functional theory (DFT) method. The impact of the co-existing acidic group of HSO₄⁻ as well as the solvent effects of the mixed acids on the hydrolysis of NMP are elucidated and discerned, and the proposed catalysis and promotion of the hydrolysis of NMP with HSO₄⁻ are verified. The HSO₄⁻-catalyzed hydrolysis pathway is more favorable than the direct pathway as well as the H₂O-catalyzed hydrolysis, indicating that HSO₄⁻ may be a promising catalyst for the preparation of FOX-7 in a mixed acid system. The present study is expected to provide a better understanding of the hydrolysis of NMP, and will significantly help with better preparation of FOX-7 and other nitro-energetic materials.

Unique and incredible catalysis of the titled hydrolysis using HSO₄⁻ is proposed and verified in the gas and solvent phases.     

In situ gelation of aqueous sulfuric acid solution for fuel cells

Aqueous sulfuric acid solution is a versatile liquid electrolyte for electrochemical applications and gelation of it has the advantages of easy shaping and reduced leaking. Herein, aqueous sulfuric acid solutions with concentrations of 1–4 mol L⁻¹ are fabricated into gel membranes by in situ polymerization of acrylamide as a monomer and divilynbenzene as a crosslinker for fuel cell applications. The gel membrane with an acid concentration of 3.5 mol L⁻¹ exhibited the maximum proton conductivity of 184 mS cm⁻¹ at 30 °C. Tensile fracture strength of the gel membrane reached 53 kPa with a tensile strain of 14. Thermogravimetric analysis reveals that the gel membranes are thermally stable at temperatures up to 231 °C. The gel membranes are successfully assembled into fuel cells and a peak power density of 74 mW cm⁻² is achieved. The fuel cell maintains steady operation over 200 h. In situ gelation of aqueous sulfuric acid solution offers an efficient strategy to prepare gel electrolytes for electrochemical devices.

In situ polymerization with acrylamide (AM) as the monomer and divinylbenzene (DVB) as a crosslinker in aqueous sulfuric acid solution resulted in gel membranes applicable in fuel cells.     

Cancer antigen 125 assessment using carbon quantum dots for optical biosensing for the early diagnosis of ovarian cancer

Fluorometric quantification of biological molecules is a key feature used in many biosensing studies. Fluorescence resonance energy transfer (FRET) using highly fluorescent quantum dots offers highly sensitive detection of the in-proximity wide variety of analyst molecules. In this contribution, we report the use of carbon quantum dots (CDs) for the ultrasensitive optical biosensing of cancer antigen 125 (CA-125) in the early malignant stage. This approach is based on monitoring the quenching of CDs luminescence at 535 nm by CA-125 after excitation at 425 nm and pH 10. The calibration of this method was performed in the concentration range of CA-125 from 0.01 to 129 U ml⁻¹ (R² = 0.99) with a detection limit of 0.66 U ml⁻¹, which matches remarkably with the standard chemiluminometric method in control and real patient samples. The sensing mechanism for cancer antigen 125 assessment was discussed on the basis of fluorescence quenching of CDs and time-resolved photoluminescence spectroscopy. The current method is easy, sensitive, cost-effective and provides a wide range of validity, which helps in overcoming the limitations of high cost and time consumption exhibited by many other traditional clinical assays for CA-125 quantification.

Fluorometric quantification of biological molecules is a key feature used in many biosensing studies.     

Rice husk biochar modified-CuCo2O4 as an efficient peroxymonosulfate activator for non-radical degradation of organic pollutants from aqueous environment

A series of rice husk biochar (RHBC) modified bimetallic oxides were prepared using a simple pyrolysis method to activate peroxymonosulfate (PMS) for the degradation of acid orange G (OG). The results demonstrated that 50 mg L⁻¹ OG was completely decomposed by 1 mM PMS activated with 100 mg L⁻¹ RHBC–CuCo₂O₄ within 15 min at initial pH 3.4. The OG degradation rate constant k of RHBC–CuCo₂O₄/PMS (0.95 × 10⁻¹ min⁻¹) was five times greater than that of CuCo₂O₄/PMS (0.19 × 10⁻¹ min⁻¹), suggesting that the introduction of RHBC significantly improved the activity of bimetallic oxides. The effects of the initial pH, catalyst dosage, PMS concentration and reaction temperature on OG removal were also studied. The degradation products of OG were analysed using a gas chromatography-mass spectrometer (GC-MS). Electron paramagnetic resonance (EPR) and quenching experiments showed that singlet oxygen (¹O₂) was the main active species. The RHBC–CuCo₂O₄/PMS oxidation system is not only unaffected by inorganic anions (Cl⁻, NO₃⁻, HCO₃⁻) and humic acid (HA), but also could remove other typical pollutants of acetaminophen (ACT), sulfathiazole (STZ), rhodamine B (RhB), and bisphenol A (BPA). These findings show that RHBC–CuCo₂O₄ has great potential for practical applications in the removal of typical organic pollutants.

A series of rice husk biochar (RHBC) modified bimetallic oxides were prepared using a simple pyrolysis method to activate peroxymonosulfate (PMS) for the degradation of acid orange G (OG).     

Facile synthesis of dual-emission fluorescent carbon nanodots for a multifunctional probe

In this study, we developed a facile method for synthesizing dual-emission carbon nanodots (CDs) through trimesic acid and o-phenylenediamine through electrolysis for 2 h. The synthesized CDs were mainly 3–7 nm in size, with an average size of 5.17 nm. The dual-emission fluorescent property of these CDs could be observed under two different excitation wavelengths. The green emission of the CDs could be quenched after the addition of mercury ions or copper ions, and the blue emission of the CDs could be inhibited using hydroxychloroquine (HCQ). Furthermore, the quenched fluorescence of CDs/Cu²⁺ could be recovered through the addition of glyphosate. We developed a multifunctional chemical sensor by using these special fluorescence materials. Under optimal conditions, the detection limits of mercury ions, glyphosate, and HCQ were 0.42 μM, 1.1 mg L⁻¹, and 0.14 μM, respectively. Moreover, this method can be used to detect mercury ions, glyphosate, and HCQ in environmental water, cereals, and urine samples, respectively.

The synthetic procedure and the applications of CDs.     

Mechanism and kinetic study of the reaction of benzoic acid with OH,NO3 and SO4− radicals in the atmosphere

Benzoic acid (BA) is one of the most common organic acids in the Earth’s atmosphere and an important component of atmospheric aerosol particles. The reaction mechanism of OH, NO₃ and SO₄⁻ radicals with BA in atmospheric water droplets and that of OH radicals with BA in the atmosphere were studied in this paper. The results show that in atmospheric water droplets the potential barriers of the elementary addition reactions of BA with OH radicals are lower than those of elementary abstraction reactions, and the potential barriers of OH-initiated reactions are less than for NO₃ and SO₄⁻ reactions. The initiation reactions of OH radicals and BA are exothermic, but the abstraction reactions of NO₃ and SO₄⁻ are endothermic processes. Among the products, 6-hydroxybenzoic acid (6-HBA) and 4,6-dihydroxybenzoic acid (4,6-DHBA) are the most stable, while 3-hydroxybenzoic acid (3-HBA) and 3,5-dihydroxybenzoic acid (3,5-DHBA) are much less stable and, thus, much less abundant compared to 6-HBA and 4,6-DHBA. The initiation and subsequent degradation of BA with OH radicals in the gas phase were calculated. The products of addition and abstraction reactions of BA with OH radicals can be further oxidized and degraded by O₂/NO. According to the results of kinetic calculations, the total reaction rate constant of OH radicals with BA at 298.15 K in atmospheric water droplets is 2.35 × 10⁻¹¹ cm³ per molecule per s. The relationship between reaction rate constants, temperature and altitude were also investigated and discussed in the present study.

We present a study of benzoic acid with OH, NO³ and SO₄⁻ radicals in the atmospheric environment.     

Anti-corrosion porous RuO2/NbC anodes for the electrochemical oxidation of phenol

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation. However, the use of these materials is often limited due to their poor corrosion resistance. Herein, we report a facile scale-up method, by carbothermal reduction, for the preparation of porous niobium carbide to be used as an anode for the electrochemical oxidation of phenol in water. No niobium ions were detected when the anodes were under aggressive attack by sulfuric acid and under electrochemical corrosion tests with a current density less than 20.98 mA cm⁻². The porous niobium carbide was further modified by applying a ruthenium oxide coating to improve its catalytic activity. The removal rates of phenol and chemical oxygen demand by the RuO₂/NbC anode reached 1.87 × 10⁻² mg min⁻¹ cm⁻² and 6.33 × 10⁻² mg min⁻¹ cm⁻², respectively. The average current efficiency was 85.2%. Thus, an anti-corrosion, highly catalytically active and energy-efficient porous RuO₂/NbC anode for the degradation of aqueous phenol in wastewater was successfully prepared.

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation.     

Crystallization of colourless hexanitratoneptunate(iv) with anhydrous H+ countercations trapped in a hydrogen bonded polymer with diamide linkers

Colourless crystalline compounds of centrosymmetric [Np(NO₃)₆]²⁻ were yielded from 3 M HNO₃ aq in the presence of double-headed 2-pyrrolidone derivatives (L). In the obtained crystal structures, H⁺ was also involved as a countercation to compensate for the negative charge of [Np(NO₃)₆]²⁻, where the initial hydration around H⁺ was fully removed during crystallization despite it having the strongest hydration enthalpy. Instead, this anhydrous H⁺ was captured by L to form a [H⁺⋯L]_n hydrogen bonded polymer. In [Np(NO₃)₆]²⁻, the Np⁴⁺ centre is twelve-coordinated with 6 bidentate NO₃⁻, and therefore, present in an icosahedral geometry bearing inversion centre. In such a centrosymmetric system, any f–f transitions stemming from the 5f³ electronic configuration of Np⁴⁺ are electric-dipole forbidden. This is the reason why the compounds currently obtained were colourless unlike ordinary Np(iv) species, which are olive-green.

Centrosymmetric hexanitratoneptunate(iv) crystallizes with anhydrous proton countercations trapped in a hydrogen bonded polymer with diamide linker molecules to give colourless crystals.