Polyvinylchloride-derived N,S co-doped carbon as an efficient sulfur host for high-performance Li–S batteries

The intrinsic polysulfide shuttle in lithium–sulfur (Li–S) batteries have significantly limited their practical applications. Conductive carbon materials with heteroatom doping and rich porosity is the most common strategy for the effective prevention of polysulfide shuttle, but are usually obtained with high costs and tedious procedures. Herein, we managed to obtain highly porous N, S-codoped carbon materials (NS-C) through treating waste plastic of polyvinylchloride (PVC) with KOH. The resulting NS-C was revealed to be highly efficient hosts for sulfur cathode, achieving large reversible capacities of 1205 mA h g⁻¹ and 836 mA h g⁻¹ at 0.1C and 1.0C, respectively, and remaining at 550 mA h g⁻¹ after 500 cycles at 1C rate, showing an outstanding cycling stability. The significantly enhanced cycling performance was mainly ascribed to both the hierarchically porous structure and heavy N, S co-dopants, which respectively provided physical blocks and chemical affinity for the efficient immobilization of intermediate lithium polysulfides. The results provide an effective paradigm in the surface chemistry and sulfur cathode materials design for high-performance Li–S batteries and a new application for recycled plastic waste.

The intrinsic polysulfide shuttle in lithium–sulfur (Li–S) batteries have significantly limited their practical applications.     

Influence of low Bi contents on phase transformation properties of VO2 studied in a VO2:Bi thin film library

A thin-film materials library in the system V–Bi–O was fabricated by reactive co-sputtering. The composition of Bi relative to V was determined by Rutherford backscattering spectroscopy, ranging from 0.06 to 0.84 at% along the library. The VO₂ phase M1 was detected by X-ray diffraction over the whole library, however a second phase was observed in the microstructure of films with Bi contents > 0.29 at%. The second phase was determined by electron diffraction to be BiVO₄, which suggests that the solubility limit of Bi in VO₂ is only ∼0.29 at%. For Bi contents from 0.08 to 0.29 at%, the phase transformation temperatures of VO₂:Bi increase from 74.7 to 76.4 °C by 8 K per at% Bi. With X-ray photoemission spectroscopy, the oxidation state of Bi was determined to be 3+. The V⁵⁺/V⁴⁺ ratio increases with increasing Bi content from 0.10 to 0.84 at%. The similarly increasing tendency of the V⁵⁺/V⁴⁺ ratio and T_c with Bi content suggests that although the ionic radius of Bi³⁺ is much larger than that of V⁴⁺, the charge doping effect and the resulting V⁵⁺ are more prominent in regulating the phase transformation behavior of Bi-doped VO₂.

A VO₂:Bi thin-film library was fabricated by reactive co-sputtering. The phase transformation temperature of VO₂:Bi increases from 74.7 to 76.4 °C by 8 K/at% Bi in the range of 0.08–0.29 at% suggesting an effect of charge doping from Bi³⁺.     

Sustainable rose multiflora derived nitrogen/oxygen-enriched micro-/mesoporous carbon as a low-cost competitive electrode towards high-performance electrochemical supercapacitors

Cost-efficient carbonaceous materials have been utilized extensively for advanced electrochemical supercapacitors. However, modest gravimetric/volumetric capacitances are the insuperable bottleneck in their practical applications. Herein, we develop a simple yet scalable method to fabricate low-cost micro-/mesoporous N/O-enriched carbon (NOC-K) by using natural rose multiflora as a precursor with KOH activation. The biomass-derived NOC-K is endowed with a large surface area of ∼1646.7 m² g⁻¹, micro-/mesoporosity with ∼61.3% microporosity, high surface wettability, and a high content of N (∼1.2 at%)/O (∼26.7 at%) species. When evaluated as an electroactive material for supercapacitors, the NOC-K electrode (5 mg cm⁻²) yields large gravimetric/volumetric specific capacitances of ∼340.0 F g⁻¹ (∼238.0 F cm⁻³) at 0.5 A g⁻¹, and even ∼200.0 F g⁻¹ (∼140.0 F cm⁻³) at 5.0 A g⁻¹, a low capacitance decay of ∼4.2% after 8200 consecutive cycles, and a striking specific energy of ∼8.3 W h kg⁻¹ in aqueous KOH electrolyte, benefiting from its intrinsic structural and compositional superiorities. Moreover, a remarkable specific energy of ∼52.6 W h kg⁻¹ and ∼96.6% capacitance retention over 6500 cycles for the NOC-K based symmetric cell are obtained with the organic electrolyte. More promisingly, the competitive NOC-K demonstrates enormous potential towards advanced supercapacitors both with aqueous and organic electrolytes as a sustainable electrode candidate.

Hierarchical micro-/mesoporous N/O-enriched carbon was scalably fabricated, and exhibited high gravimetric/volumetric capacitances, a large energy density and long-term cycling stability for supercapacitors with aqueous and organic electrolytes.     

Sensitive electrochemical sensor based on poly(l-glutamic acid)/graphene oxide composite material for simultaneous detection of heavy metal ions

Heavy metal pollution can be toxic to humans and wildlife, thus it is of great significance to develop rapid and sensitive methods to detect heavy metal ions. Here, a novel type of electrochemical sensor for the simultaneous detection of heavy metal ions has been prepared by using poly(l-glutamic acid) (PGA) and graphene oxide (GO) composite materials to modify the glassy carbon electrode (GCE). Due to the good binding properties of poly(l-glutamic acid) (PGA) for the heavy metal ions (such as Cu²⁺, Cd²⁺, and Hg²⁺) as well as good electron conductivity of graphene oxide (GO), the heavy metal ions, Cu²⁺, Cd²⁺, and Hg²⁺ in aqueous solution can be accurately detected by using differential pulse anodic stripping voltammetry method (DPASV). Under the optimized experiment conditions, the modified GCE shows excellent electrochemical performance toward Cu²⁺, Cd²⁺, and Hg²⁺, and the linear range of PG/GCE for Cu²⁺, Cd²⁺, and Hg²⁺ is 0.25–5.5 μM, and the limits of detection (LODs, S/N ≥ 3) Cu²⁺, Cd²⁺, and Hg²⁺ are estimated to be 0.024 μM, 0.015 μM and 0.032 μM, respectively. Moreover, the modified GCE is successfully applied to the determination of Cu²⁺, Cd²⁺, and Hg²⁺ in real samples. All obtained results show that the modified electrode not only has the advantages of simple preparation, high sensitivity, and good stability, but also can be applied in the field of heavy metal ion detection.

A novel electrochemical sensor with high stability and good reproducibility for the simultaneous detection of heavy metal ions was prepared by using PGA/GO to modify the GCE, showing high sensitivity of superior to most of the reported values.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

Coronene diimide-based ‘bowl’ nanostructures as red emitters for the analysis of latent fingerprints and metal ion detection

We report an NIR-based photoluminescent material, namely benzo-coronene diimide (CDI 2), and its use in the visualization of latent fingerprints (LFPs) and in the metal ion detection in an aqueous medium. CDI 2 exhibited nano-sized interlinked fibre structures forming ‘bowl’ shaped nanoarchitectures as red emitters with the Commission Internationale de l''Eclairage (CIE) coordinates (x, y) of (0.67, 0.33) with 100% colour purity in the solid state. CDI 2 was confirmed to be the potential candidate for the analysis of LFPs and the detection of Pd²⁺/Cu²⁺ in an aqueous medium.

We report CDI 2 as a red emitter (CIE 0.67, 0.33) with 100% colour purity in the solid state forming a ‘bowl’ shaped nanoarchitecture and its use in the visualization of latent fingerprints and in the metal ion detection in an aqueous medium.

Nowadays, latent (invisible) fingerprints are utilized as a personal identification mark in numerous instances to decrypt information during criminal and forensic investigations, to access computers and equipments utilized for administrative purposes, to provide aid in health and medical facilities, to mark the attendance of employees in government and private institutes and to monitor the entry/exit in security rooms owing to national interest.^1,2 Each and every individual, even the identical twins, have a unique pattern of friction ridges formed from the epidermis of the fingertips.³ Different imaging techniques are used to visualize the LFPs; however, low resolution, destruction of the fingerprints during the analysis and low sensitivity of these techniques reduce the effectiveness of the LFPs.^4–6 The power-dusting technique, which involves the use of NIR-photoluminescent materials, emerged as a new advanced approach to develop the latent fingerprints.^7,8The availability of fluorescent red emitters is relatively limited in comparison with green and blue emitters for their application in organic light emitting diodes (OLEDs) due to their colour impurities.⁹ According to previous literature, red OLEDs are available, which are based on either organometallic complexes or organic materials, such as dicyanomethylene, polyarene and chromene dopants.^10a,b Therefore, the focus of the current research is in developing new red emitters for LFPs and metal ion sensing.^11a,b Blue, green and red emitters are equally essential for the generation of white light. However, research over the past decade demonstrated high external quantum efficiencies of green and red emitters with a high colour purity and brightness compared with those of the blue triplet emitters. The characteristics of saturated red emission, spectral stability and stable electroluminescence efficiency of red emitters at high brightness and current enable them to be used as an emitting species in OLEDs. Herein, we report on benzocoronene^12,13 (CDI 2), which exhibited a highly conjugated π-system with emission extended to the red region (red emitters).^14,15CDI 2 (Fig. 1a) exhibited nano-sized interlinked fibre structures forming a ‘bowl’ like nanoarchitecture and was used to lift the LFPs developed on glass, metal, or aluminium surfaces. The CIE 1931 (RGB) coordinates¹⁶ demonstrated a 100% colour purity in the solid state and on LFPs. CDI 2 could be a potential candidate for the detection of Pd²⁺/Pd⁰ in water.Open in a separate windowFig. 1(a) Structure of the CDI 2 derivative; (b) energy optimized structure of CDI 2; (c) molecular plots of HOMO and LUMO of CDI 2 using the DFT calculation at the B3LYP/6-31G* basis set; (d) cyclic voltammogram (CV) of CDI 2 (0.2 mM) in the CH₂Cl₂ solvent; supporting electrolyte 0.1 mol L⁻¹ TBAP; scan rate 0.05 V s⁻¹; potential range of −1.6–2.0 V vs. Ag/Ag⁺ electrode; (e) TGA curve of CDI 2; (f) emission spectrum of the fluorescent powder CDI 2; (g) CIE-1931 plots corresponding to the emission data of (f); (h) emission spectra of CDI 2 (10 μM) in different ratios of H₂O and DMSO (λ_ex = 450 nm, slit width (ex/em) = 5/5) [inset of 1f showing photograph of CDI 2 as solid powder; inset of 1 h showing CIE plot of various water ratios].The preparation of the building block commenced with the Suzuki coupling reaction of 1-bromo-N,N′-di-(3-pentyl)-perylene 3,4,9,10-tetracarboxylic diimide with 4-formylphenylboronic acid, which was then subjected to condensation with hydroxylamine hydrochloride (Schiff-base condensation). Subsequent propargylation with propargyl bromide provided PDI 1 in good yield.^11bCDI 2 was subsequently obtained through the photocyclization of PDI 1 in CH₃CN (96% yield). The chemical structure of CDI 2 was elucidated explicitly via 1D NMR (¹H and ¹³C), 2D NMR (COSEY) and FTIR techniques (Fig. S1a–e^†). CDI 2 exhibited solubility in common organic solvents. The thermal stability of CDI 2 was measured via the thermogravimetric analysis (TGA). CDI 2 showed an initial mass loss of ∼35% in the temperature range of 170–450 °C. This mass loss corresponds to the removal of propargyl and oxime moieties from CDI 2. The decomposition temperature (T_d, 60% weight loss) of CDI 2 was found to be 550 °C (Fig. 1e).The computational study was performed at the B3LYP/6-31G* basis level using the Gaussian 09 software. The contour picture of HOMO/LUMO revealed that the electron density of the HOMO localized predominately on the π-conjugated benzocoronene and oxygen heteroatom of the oxime moiety, while that of LUMO was mainly distributed on the benzocoronene part. The calculated HOMO and LUMO energy levels were −6.03 and −3.43 eV, respectively. The band gap energy in CDI 2 was 2.59 eV (Fig. 1b, c, S2^† and ​and3a3a).Open in a separate windowFig. 3(a) The fluorescent imaging of LFPs on nonporous surfaces developed with a near-infrared fluorescent compound, namely, CDI 2 powder. (i) Spatula; (ii) glass slide; (iii) silver foil; and (iv) metal piece under irradiation by 365 nm UV lamp. (b) Photographs of the LFPs developed with the CDI 2 powder to visualize the latent fingerprints on (i) glass slide and (iii) metal piece; (ii) and (iv) variation in the gray value over the LFP shown by the white line shown in panels (i) and (iii), respectively. (c) Fluorescence image of LFP developed using the CDI 2 powder-dusting method on the aluminium foil with a 2nd level information providing areas, such as (1) core, (2) ridge termination, (3) ridge bifurcation, (4) bridge, (5) lake and (6) island.In cyclic voltammetry, CDI 2 exhibited an onset reduction (E_red) and weak oxidation potential (E_ox) values of 0.56 V and 1.39 V, respectively. The HOMO and LUMO energy levels calculated using the formula E_LUMO = −[E_red(onset) + 4.4] eV and E_HOMO = −[E_ox(onset) + 4.4] eV from experimentally determined E_ox and E_red values were −5.80 eV and −3.43 eV, respectively, which were in line with the HOMO–LUMO energies calculated via the density functional theory (Fig. 1d). The onset reduction peaks at −1.39 V and −1.6 V could be assigned to the second and third reductions of CDI 2 characteristic for the π-conjugated system.The introduction of more planar groups into CDI 2 shifted the solid-state emission (powder form and thin film) to the red region with a λ_em of 660 nm (Fig. 1f) and a photoluminescence quantum yield of 3.89%. The emission wavelength of CDI 2 was further complimented by considering the CIE-1931 RGB colour coordinates. The colour purity¹⁷ of CDI 2 in the powder form was calculated using the following equation:where (x_s, y_s) are the coordinates of the CDI 2 sample at an emission wavelength of 650 nm, whereas (x_d, y_d) and (x_i, y_i) are the coordinates of the illumination point. The CIE-1931 RGB colour coordinates (0.67, 0.33) of CDI 2 (Fig. 1g) in the powder form and after deposition on the thin film exhibited a 100% colour purity for red emission, and it could be used as a red emitter in organic light emitting diodes (OLEDs). The colour purity of PDI I (as control) in the solid state was 84% (Fig. S4^†).The red photoluminescence of CDI 2 encouraged us to investigate the possibility of their AIE properties. The AIE feature of CDI 2 was evaluated by measuring its photoluminescence spectra in a binary mixture of DMSO–H₂O with different water fractions (f_w). The emission maxima of CDI 2 exhibited a red shift from 530 to 640 nm with an increase in f_w, revealing the formation of nanoaggregates. When f_w was increased to 20%, the ratiometric (I_{640 nm}/I_{530 nm}) photoluminescence intensity of CDI 2 gradually changed. Afterwards, large ratiometric changes (∼14-fold) were observed for f_w up to 80% (Fig. 1h). Accordingly, we prepared a solution of CDI 2 in DMSO for comparison. As expected, the photoluminescence and the UV-vis spectra of CDI 2 recorded in DMSO showed an emission wavelength only at 530 nm and an absorption peak at 474/508 nm (Fig. S5 and S11^†). In DMSO, the Franck–Condon progression value A_0–0/A_0–1 ≈ 1.34 indicated a monomer state of CDIs, whereas a value of A_0–0/A_0–1 of ≤0.7 in a 90% water–DMSO mixture indicated an aggregated state of PDIs (Table S1^†).Complimenting the UV-vis and the fluorescence changes on a supramolecular level, we performed an AFM imaging of thin films prepared on a glass surface using a 10 μM solution of CDI 2 in DMSO and H₂O–DMSO (f_w = 50% and 90%) (Fig. 2a–d). In DMSO, the formation of oval shape aggregates with a diameter in the range of 240–300 nm over a large surface area was observed (Fig. S6a^†). In a 50% H₂O–DMSO binary mixture, the oval aggregates deproliferated into smaller structures and an invariant background of oval and sphere aggregates was detected and their diameters slightly decreased to 90–200 nm (Fig. S6b and c^†).Open in a separate windowFig. 2AFM micrographs of CDI 2 in (a) DMSO, (b) 50% H₂O/DMSO mixture, (c) 90% H₂O/DMSO mixture and (d) magnified view of (c) showing different morphologies and extracted height profile, size graph of CDI 2; DLS bar graph (number percent) of CDI 2 in (e) DMSO, (f) 50% H₂O/DMSO mixture and (g) 90% H₂O/DMSO mixture.Interestingly, in a 90% H₂O–DMSO mixture, the changes in the structures occurred, and we detected a nano-sized interlinked fibre arranged in such a fashion that it formed a ‘bowl’ like nano-architecture with a central cavity inside. The invariant clusters of fibres detected on the surface were 70–110 nm in diameter (Fig. 2c and d). The hollow cavity in the centre exhibited a diameter of 138 nm and a depth of ∼2–3 nm (Fig. S6d–f^†). We further recorded the dynamic light scattering data for these nanoaggregates in H₂O–DMSO binary mixtures (Fig. 2e–g). In DMSO, CDI 2 displayed a diameter in the range of 190–530 nm with Z-average and polydispersity index (PDI) values of 353 nm and 0.24, respectively. In the 50% H₂O–DMSO mixture, the size of the aggregates lay in two different sizes, i.e. 50–120 nm and 220–531 nm (PDI = 0.29). In the 90% H₂O–DMSO mixture, the size of the nanoaggregates decreased to 80–165 nm, which was in concordance with the AFM data.The use of near IR-based fluorescent materials in the powder-dusting method for the visualization of LFPs was a simple and non-destructive tool and did not require rigorous post-treatment method (Fig. 3). We applied our CDI 2 for the development of LFPs on porous and non-porous surfaces, such as ceramic floor tiles, glass, metals, and aluminium foils (Fig. 3a). In all cases, we obtained good quality LFPs to extract information of the ridge pattern (Ist level) and minutae details, such as ridge termination, bifurcation, core, island, lake, and bridge (2nd level) (Fig. 3c). The photoluminescence contrast between the papillary ridges and furrows was analysed by examining the cross-sectional view. The gray value varied significantly over the line/imaginary white line extended on LFPs, thereby clearly showing a discrimination between the ridges and furrows in terms of fluorescence contrast in LFPs (Fig. 3b). The solid-state emission of CDI 2 was also recorded by directly placing the fingerprint stamped substrate in the spectrofluorometer. The solid-state emission spectrum showed high emission intensity at 660 nm in accordance with the emission maximum of CDI 2 in solution form. The solid-state emission wavelength of CDI 2 was further complimented by considering the CIE-1931 RGB colour coordinates. The CIE-1931 RGB colour coordinates (0.67, 0.33) of CDI 2 on developed LFPs showed 100% colour purity (Fig. 4).Open in a separate windowFig. 4(a) Emission spectrum of LFP developed with the CDI 2 powder over a glass slide and (b) CIE-1931 plots corresponding to emission data of (a).Given that CDI 2 possessed good emission properties in the solution as well as it contained an oxime group coupled with a propargyl group, CDI 2 provided heteroatom binding sites, such as O and N. The sensing behaviour of CDI 2 in the DMSO : HEPES buffer (1 : 9, pH = 7.2) towards numerous metal cations was examined. The fluorescence intensity of CDI 2 (5 μM) at 640 nm exhibited no detectable changes, whereas the quenching of the fluorescence intensity was observed for Cu²⁺ ions and Pd⁰/Pd²⁺ species (Fig. S7^†). Later, the detailed response of CDI 2 towards Cu²⁺ ions and Pd⁰/Pd²⁺ species in a 90% aqueous medium was investigated. CDI 2 (5 μM) exhibited an emission band at 640 nm in the DMSO : HEPES buffer (1 : 9, pH = 7.2, 10⁻² M) upon excitation at 450 nm. Upon addition of a Pd⁰/Pd²⁺ solution (25 μM for Pd⁰/50 μM for Pd²⁺) to CDI 2 in a 90% buffered medium, the emission intensity at 640 nm was quenched. The Stern–Volmer constant (K_SV) values calculated for Pd⁰ and Pd²⁺ were 1.74 × 10⁶ M⁻¹ and 1.79 × 10⁶ M⁻¹, respectively. The fluorescence response of CDI 2 towards Pd²⁺/Pd⁰ exhibited a linear relationship (Fig. S8 and S9;^†R² = 0.98 for Pd⁰/Pd²⁺) between the concentration of Pd⁰/Pd²⁺ (0–1 × 10⁻⁷ M for Pd⁰ and 0–1.5 × 10⁻⁷ M for Pd²⁺) and the I/I₀ ratio of the fluorescence intensity. The lowest detection limits (LOD) calculated for CDI 2 towards Pd⁰ and Pd²⁺ species were 86.1 nM and 83.9 nM, respectively (Fig. S8 and S9^†). Similarly, CDI 2 (5 μM) could also detect Cu²⁺ ion in the DMSO : HEPES buffer (1 : 9, pH = 7.2, 10⁻² M) (Fig. S10^†). The Cu²⁺ ions tended to bind to the heteroatom binding sites, such as O and N of CDI 2. The Stern–Volmer constant (K_SV) value for Cu²⁺ was found to be 1.2 × 10⁶ M⁻¹. The quenching of the fluorescence intensity showed a linear correlation of I/I₀ ratio at 640 nm vs. Cu²⁺ concentration (0–1 × 10⁻⁷ M) with a good correlation (R² = 0.9912) and a minimal detection limit of 124 nM.In conclusion, CDI 2 based ‘bowl’ nanostructures could be a potential candidate for use as red emitters with a 100% colour purity for OLED applications. CDI 2 was best for the analysis of latent fingerprints and the detection of important metal ions in a >90% aqueous medium by following the fluorescence approach.     

Metal oxide QD based ultrasensitive microsphere fluorescent sensor for copper,chromium and iron ions in water

Herein we developed a rapid, cheap, and water-soluble ultra-sensitive ZnO quantum dot (QD) based metal sensor for detecting different hazardous metal ions up to the picomolar range in water. Various spectroscopic and microscopic techniques confirmed the formation of 2.15 ± 0.46 μm of ZnO QD conjugated CMC microspheres (ZCM microspheres) which contain 5.5 ± 0.5 nm fluorescent zinc oxide (ZnO) QDs. Our system, as a promising sensor, exhibited excellent photostability and affinity towards various heavy metal ions. The detection limits were calculated to be 16 pM for Cu²⁺ and 0.18 nM for Cr⁶⁺ ions which are better than previously reported values. The simple fluorescence ‘turn off’ property of our ZCM microsphere sensor system can serve a two-in-one purpose by not only detecting the heavy metals but also quantifying them. Nonetheless, pattern recognition for different heavy metals helped us to detect and identify multiple heavy metal ions. Finally, their practical applications on real samples also demonstrated that the ZCM sensor can be effectively utilized for detection of Cr⁶⁺, Fe³⁺, Cu²⁺ present in the real water samples. This study may inspire future research and design of target fluorescent metal oxide QDs with specific functions.

Herein we developed a rapid, cheap, and water-soluble ultra-sensitive ZnO quantum dot (QD) based metal sensor for detecting different hazardous metal ions up to the picomolar range in water.     

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.     

Super rapid removal of copper,cadmium and lead ions from water by NTA-silica gel

Copper (Cu²⁺), cadmium (Cd²⁺) and lead ions (Pb²⁺) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb²⁺ (<2 min), Cu²⁺ and Cd²⁺ (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺, respectively). At the same concentration of 20 mg L⁻¹, the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2–9) and maintained in the presence of competitive metal ions (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO₃) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu²⁺, Cd²⁺, and Pb²⁺ from contaminated aquatic environments.

A silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple method for the super rapid removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water.     

Porous BMTTPA–CS–GO nanocomposite for the efficient removal of heavy metal ions from aqueous solutions

In this study, a stable, cost-effective and environmentally friendly porous 2,5-bis(methylthio)terephthalaldehyde–chitosan–grafted graphene oxide (BMTTPA–CS–GO) nanocomposite was synthesized by covalently grafting BMTTPA–CS onto the surfaces of graphene oxide and used for removing heavy metal ions from polluted water. According to well-established Hg²⁺–thioether coordination chemistry, the newly designed covalently linked stable porous BMTTPA–CS–GO nanocomposite with thioether units on the pore walls greatly increases the adsorption capacity of Hg²⁺ and does not cause secondary pollution to the environment. The results of sorption experiments and inductively coupled plasma mass spectrometry measurements demonstrate that the maximum adsorption capacity of Hg²⁺ on BMTTPA–CS–GO at pH 7 is 306.8 mg g⁻¹, indicating that BMTTPA–CS–GO has excellent adsorption performance for Hg²⁺. The experimental results show that this stable, environmentally friendly, cost-effective and excellent adsorption performance of BMTTPA–CS–GO makes it a potential nanocomposite for removing Hg²⁺ and other heavy metal ions from polluted water, and even drinking water. This study suggests that covalently linked crucial groups on the surface of carbon-based materials are essential for improving the adsorption capacity of adsorbents for heavy metal ions.

Novel porous BMTTPA–CS–GO nanocomposites are prepared by covalently grafting BMTTPA–CS onto GO surfaces, and used for efficient removal of heavy metal ions from polluted water.     

Novel mesoporous Co3O4–Sb2O3–SnO2 active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄–Sb₂O₃–SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET)/Barrett–Joyner–Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄–Sb₂O₃–SnO₂ showed a high specific capacity of 96 and 124 F g⁻¹ at the scan rate of 10 mV s⁻¹, respectively. In addition, the newly-developed electrode AC/Co₃O₄–Sb₂O₃–SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s⁻¹. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g⁻¹ at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm⁻¹. The electrode displayed a high ion removal rate of 7.1 mg g⁻¹ min⁻¹ with an excellent desalination–regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes.     

Acetylacetone functionalized magnetic carbon microspheres for the highly-efficient adsorption of heavy metal ions from aqueous solutions

Herein, Acac-C@Fe₃O₄, a magnetic carbon (C@Fe₃O₄) modified with acetylacetone (Acac), was first prepared and used as a solid-phase adsorbent for adsorbing some heavy metal ions from aqueous solution. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and BET studies. Some parameters affecting the adsorption and desorption processes were studied in Pb²⁺ solution, including sample pH, contact time, initial concentration, type and connection of the desorption solution. Absorption results showed that removal of Pb²⁺ was 100% under optimal conditions at an initial concentration of 10.0 mg L⁻¹. The adsorption mechanism conformed well to a pseudo-second order kinetic model. The adsorption capacity of the sorbent also showed promising results with Hg²⁺, Cr³⁺, Fe²⁺, Cd²⁺, Mn²⁺, Zn²⁺, Cu²⁺ and Pb²⁺, where maximum adsorption capacities reached 98.0, 151.2, 188.9, 202.2, 286.3, 297.2, 305.1 and 345.3 mg g⁻¹, respectively. The Acac-C@Fe₃O₄ microsphere material was successfully applied to the adsorption of heavy metal ions in aqueous solution.

Herein, Acac-C@Fe₃O₄, a magnetic carbon (C@Fe₃O₄) modified with acetylacetone (Acac), was first prepared and used as a solid-phase adsorbent for adsorbing some heavy metal ions from aqueous solution.     

Uptake of heavy metal ions from aqueous media by hydrogels and their conversion to nanoparticles for generation of a catalyst system: two-fold application study

Poly(methacrylic acid) (P(MAA)), poly(acrylamide) (P(AAm)) and poly(3-acrylamidopropyltrimethyl ammonium chloride) (P(APTMACl)) were synthesized as anionic, neutral and cationic hydrogels, respectively. The synthesized hydrogels have the ability to be used as absorbents for the removal of selected heavy metal ions such as Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ from aqueous media. Absorption studies revealed that the absorption of metal ions by the hydrogels followed the order Cu²⁺ > Ni²⁺ > Co²⁺ > Zn²⁺. For the mechanism of absorption, both Freundlich and Langmuir absorption isotherms were applied. Metal ion entrapped hydrogels were treated using an in situ chemical reduction method in order to convert the metal ions into metal nanoparticles for the synthesis of hybrid hydrogels. The synthesis and morphology were confirmed using FT-IR and SEM, while the absorbed metal amounts were measured using TGA and AAS. The hybrid hydrogels were further used as catalysts for the reduction of macro (methylene blue, methyl orange and congo red) and micro (4-nitrophenol and nitrobenzene) pollutants from the aqueous environment. The catalytic performance and re-usability of the hybrid hydrogels were successfully investigated.

Poly(methacrylic acid) (P(MAA)), poly(acrylamide) (P(AAm)) and poly(3-acrylamidopropyltrimethyl ammonium chloride) (P(APTMACl)) were synthesized as anionic, neutral and cationic hydrogels respectively.     

Metal–organic frameworks (MOFs) based nanofiber architectures for the removal of heavy metal ions

Environmental heavy metal ions (HMIs) accumulate in living organisms and cause various diseases. Metal–organic frameworks (MOFs) have proven to be promising and effective materials for removing heavy metal ions from contaminated water because of their high porosity, remarkable physical and chemical properties, and high specific surface area. MOFs are self-assembling metal ions or clusters with organic linkers. Metals are used as dowel pins to build two-dimensional or three-dimensional frameworks, and organic linkers serve as carriers. Modern research has mainly focused on designing MOFs-based materials with improved adsorption and separation properties. In this review, for the first time, an in-depth look at the use of MOFs nanofiber materials for HMIs removal applications is provided. This review will focus on the synthesis, properties, and recent advances and provide an understanding of the opportunities and challenges that will arise in the synthesis of future MOFs–nanofiber composites in this area. MOFs decorated on nanofibers possess rapid adsorption kinetics, a high adsorption capacity, excellent selectivity, and good reusability. In addition, the substantial adsorption capacities are mainly due to interactions between the target ions and functional binding groups on the MOFs–nanofiber composites and the highly ordered porous structure.

Metal–organic frameworks (MOFs) are promising and effective materials for removing heavy metal ions from contaminated water owing to their high porosity, remarkable physical and chemical properties, and high specific surface area.     

Conversion of plastic waste into fuel oil using zeolite catalysts in a bench-scale pyrolysis reactor

Catalytic pyrolysis of mixed plastic waste to fuel oil experiment was tested with ZSM-5 zeolite (commercial and synthesized) catalysts along with other catalysts. The ZSM-5 zeolite catalyst was effectively produced using a hydrothermal technique via metakaolin as an alumina source. The catalytic pyrolysis of different types of plastic (single and multilayer) wastes in the presence of various catalysts was tested with a bench-scale pyrolysis setup with 2 kg per batch capacity. Polyolefin based plastics (low-density polyethylene, high-density polyethylene, and polypropylene), multilayer plastics such as biaxial oriented polypropylene (BOPP), metalized biaxial oriented polypropylene layers (MET BOPP), polyethylene terephthalate (PET), metalized polyethylene terephthalate (MET/PET), polyethylene terephthalate combined polyethylene (PET/PE), and mixed plastic waste collected from the corporation sorting center were pyrolyzed in a batch pyrolysis system with 1 kg feed to determine the oil, gas and char distributions. The performances of commercial ZSM-5 and lab synthesized ZSM-5 catalysts were compared for the pyrolysis of non-recyclable plastic wastes. Other commercial catalysts including mordenite and gamma alumina were also tested for pyrolysis experiments. The gross calorific value of oil obtained from different combinations of multilayer packaging waste varied between 10 789–7156 kcal kg⁻¹. BOPP-based plastic waste gave higher oil yield and calorific value than PET-based plastic waste. Sulfur content present in the oil from different plastic wastes was measured below the detection limit. The synthesized ZSM-5 zeolite catalyst produced a maximum oil output of 70% and corresponding gas and char of 16% and 14% for LDPE plastic. The strong acidic properties and microporous crystalline structure of the synthesized ZSM-5 catalyst enables increased cracking and isomerization, leading to an increased breakup of larger molecules to smaller molecules forming more oil yield in the pyrolysis experiments. Residual char analysis showed the maximum percentage of carbon with heavy metal concentrations (mg kg⁻¹) in the range of viz., chromium (15.36–97.48), aluminium (1.03–2.54), cobalt (1.0–5.85), copper (115.37–213.59), lead (89.12–217.3), and nickel (21.05–175.41), respectively.

Catalytic pyrolysis of mixed plastic waste to fuel oil experiment was tested with ZSM-5 zeolite (commercial and synthesized) catalysts along with other catalysts.     

Ionic liquid-immobilized silica gel as a new sorbent for solid-phase extraction of heavy metal ions in water samples

In the current study, we have developed a solid-phase extraction (SPE) method with novel C18-alkylimidazolium ionic liquid immobilized silica (SiO₂–(CH₂)₃–Im–C₁₈) for the preconcentration of trace heavy metals from aqueous samples as a prior step to their determination by inductively coupled plasma mass spectrometry (ICPMS). The material was characterized by Fourier-transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Energy-Dispersive X-ray Spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) analysis. A mini-column packed with SiO₂–(CH₂)₃–Im–C₁₈ sorbent was used for the extraction of the metal ions complexed with 1-(2-pyridylazo)-2-naphthol (PAN) from the water sample. The effects of pH, PAN concentration, length of the alkyl chain of the ionic liquid, eluent concentration, eluent volume, and breakthrough volume have been investigated. The SiO₂–(CH₂)₃–Im–C₁₈ allows the isolation and preconcentration of the heavy metal ions with enrichment factors of 150, 60, 80, 80, and 150 for Cr³⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Pb²⁺, respectively. The limits of detection (LODs) for Cr³⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Pb²⁺ were 0.724, 11.329, 4.571, 0.112, and 0.819 μg L⁻¹, respectively with the relative standard deviation (RSD) in the range of 0.941–1.351%.

Novel C18-alkylimidazolium ionic liquid immobilized silica (SiO₂–(CH₂)₃–Im–C₁₈) was synthesized through a four-step procedure. It showed high efficiency for the separation/preconcentration of trace heavy metal ions from aqueous samples.     

A pH-stable Ag(i) multifunctional luminescent sensor for the efficient detection of organic solvents,organochlorine pesticides and heavy metal ions

Developing novel luminescent materials for sensitive and rapid detection of heavy metal ions, organic solvents and organochlorine pesticides is vital for environmental monitoring. Herein, a new Ag(i) luminescent coordination polymer [Ag(3-dpyb)(H₃odpa)]·H₂O (LCP 1) (3-dpyb = N,N′-bis(3-pyridinecarboxamide)-1,4-butane, H₄odpa = 4,4′-oxydiphthalic acid) was obtained by a hydrothermal reaction and characterized by single crystal, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and luminescence spectroscopy. LCP 1 is a three-dimensional (3D) supramolecular framework formed from 1D [Ag-3-dpyb-H₃odpa]_n chains and H-bond interactions. The luminescence sensing study of LCP 1 for recognizing organic solvents, organochlorine pesticides and heavy metal ions was performed, which demonstrated it to be a potential luminescent sensor for Hacac, NB, 2,6-DCN, Fe²⁺, Hg²⁺, and Fe³⁺. Fe²⁺, Hg²⁺, and Fe³⁺ in river water were determined using LCP 1 with satisfying recovery.

3D supramolecular LCP 1 can detect Hacac, NB, 2,6-DCN, Fe²⁺, Hg²⁺, and Fe³⁺ with a low detection limit and pH stability.     

Solution-phase phosphorus substitution for enhanced oxygen evolution reaction in Cu2WS4

Transition metal phosphides are among the most promising materials for achieving efficient electrocatalytic performance without the use of rare or expensive noble metals. However, previous research into phosphides for the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) has focused on high-temperature vapor-phase processes, which are not practical for large-scale applications. Here, we introduce a simple, one-step solution-phase method of phosphide synthesis by modifying Cu₂WS₄ using triphenylphosphine (TPP), which serves to substitute S with P and transform the normally inactive basal plane of Cu₂WS₄ into a defect-rich, activated basal plane. The OER activity was significantly enhanced by phosphorus substitution, with the resulting Tafel slope of the sample with ∼8 at% phosphorus reaching 194 mV dec⁻¹, a result close to that of the best OER catalyst (RuO₂, 151 mV dec⁻¹). The sample possessed stable OER performance, showing no degradation in current density over ∼24 hours (500 cycles), proving the robust and stable nature of the phosphorus substitution. These results open the possibility for further phosphide catalyst development using this low-cost, solution-phase method.

Solution-phase synthesis of a transition metal phosphide for use as a highly efficient electrocatalyst.     

A novel efficient bioflocculant QZ-7 for the removal of heavy metals from industrial wastewater

In this study, a novel bioflocculant QZ-7 was produced from Bacillus salmalaya 139SI for industrial wastewater treatment. Biochemical analysis, FTIR, scanning electron microscopy-energy dispersive X-ray spectroscopy, and thermogravimetric analysis were performed. A synthetic wastewater sample was used to validate the performance of the prepared OZ-7 for the adsorption efficiency of As, Zn²⁺ Pb²⁺, Cu²⁺, and Cd²⁺ under optimal experimental conditions such as initial metal concentrations, pH, contact time (h) and QZ-7 adsorbent dosage (mg mL⁻¹). The maximum removal efficiency for Zn²⁺ (81.3%), As (78.6%), Pb²⁺ (77.9%), Cu²⁺ (76.1%), and Cd²⁺ (68.7%) was achieved using an optimal bioflocculant dosage of 60 mg L⁻¹ at 2 h shaking time, 100 rpm and pH 7. Furthermore, the obtained optimum experimental conditions were validated using real industrial wastewater and the removal efficiencies of 89.8%, 77.4% and 58.4% were obtained for As, Zn²⁺ and Cu²⁺, respectively. The results revealed that the prepared bioflocculant QZ-7 has the capability to be used for the removal of heavy metals from industrial wastewater.

In this study, a novel bioflocculant was produced using Bacillus salmalaya 139SI for industrial waste water treatment.     

Synthesis and characterization of TiO2/graphene oxide nanocomposites for photoreduction of heavy metal ions in reverse osmosis concentrate

In this study, graphene oxide (GO), titanium dioxide (TiO₂) and TiO₂/GO nanocomposites were synthesized as the catalysts for photoreduction of endocrine disrupting heavy metal ions in reverse osmosis concentrates (ROC). The morphology, structure and chemical composition of these catalysts were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Brunauer–Emmett–Teller analysis, Barrett–Joyner–Halenda, Fourier transform infrared spectroscopy and Raman spectroscopy. The photocatalytic experiments showed that TiO₂/GO nanocomposites exhibit a higher photoreduction performance than pure TiO₂ and GO. Under the optimal conditions, the removal rates of Cd²⁺ and Pb²⁺ can reach 66.32 and 88.96%, respectively, confirming the effectiveness of photoreduction to reduce the endocrine disrupting heavy metal ions in ROC resulted from the combined adsorption–reduction with TiO₂/GO nanocomposites.

TiO₂/GO nanocomposites were synthesized successfully and exhibited an excellent ability to reduce heavy metal ions in reverse osmosis concentrate.