Zn2+ removal from the aqueous environment using a polydopamine/hydroxyapatite/Fe3O4 magnetic composite under ultrasonic waves

In this study, an easily magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was suitably synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution, and its structural properties were thoroughly examined using different analytical techniques. The effect of multiple parameters like pH, ultrasonic power, ultrasonic time, adsorbent dose, and initial Zn²⁺ concentration on the adsorption efficiency was assessed using RSM-CCD. According to the acquired results, by increasing the adsorbent quantity, ultrasonic power, ultrasonic time, and pH, the Zn²⁺ adsorption efficiency increased and the interaction between the variables of ultrasonic power/Zn²⁺ concentration, pH/Zn²⁺ concentration, pH/absorbent dose, and ultrasonic time/adsorbent dose has a vital role in the Zn²⁺ adsorption. The uptake process of Zn²⁺ onto PDA/HAp/Fe₃O₄ followed Freundlich and pseudo-second order kinetic models. The maximum capacity of Zn²⁺ adsorption (q_m) obtained by PDA/HAp/Fe₃O₄, HAp/Fe₃O₄, and HAp was determined as 46.37 mg g⁻¹, 40.07 mg g⁻¹, and 37.57 mg g⁻¹, respectively. Due to its good performance and recoverability (ten times), the HAp/Fe₃O₄/PDA magnetic composite can be proposed as a good candidate to eliminate Zn²⁺ ions from a water solution.

A magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution and the structural properties were examined.     

Purification and Biochemical Characterization of α-Amylase from Radish (Raphanus sativus L.) Seeds Using Response surface methodology

The α-amylase from radish seeds has been purified to apparent homogeneity with specific activity of 821.66 U/mg of protein with 36 folds purification. The purified enzyme displayed single protein band on native PAGE (polyacrylamide gel electrophoresis) confirmed by activity staining. The SDS PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) revealed protein band of approximately 43 and 90 kDa. The calcium content of enzyme preparation was around 1.442 µg/mg of protein as analyzed by AAS (atomic absorption spectrophotometer). The energy of activation for enzyme was 3.82 kcal/moles with K_m and V_max values 4.8 mg/mL and 0.377, respectively, using starch as the substrate. The metal ions such as Ca²⁺ and Mg²⁺ showed augmented activity whereas Ni²⁺, Fe²⁺ and Cu²⁺ showed slight inhibition in the amylase activity. The thiol group reagents also activated the enzyme. Further, the effect of pH and temperature on α-amylase activity were analyzed and optimized utilizing response surface methodology. The value of regression coefficients was found significant (R² = 92.62%) showing the suitability of the proposed model. The multiple regression and analysis of variance showed the individual and cumulative effect of pH and temperature on the activity of enzyme with optimum pH of 6.5 and temperature of 60 °C. Additionally, contour plot, 3D surface plot and optimization plot were used to predict the effect of each variable with minimum set of experiments.

     

Environmental surface chemistries and adsorption behaviors of metal cations (Fe3+, Fe2+, Ca2+ and Zn2+) on manganese dioxide-modified green biochar

The facile preparation and modification of low-cost/efficient adsorbents or biochar (CP) derived from the carbonization of palm kernel cake (lignocellulosic residue) has been studied for the selective adsorption of various metal cations, such as Fe³⁺, Fe²⁺, Ca²⁺ and Zn²⁺, from aqueous solution. The CP surface was modified with KMnO₄ (CPMn) and HNO₃ (CPHNO₃) in order to improve the adsorption efficiency. The physicochemical properties of the as-prepared adsorbents were investigated via BET, pH_pzc, FT-IR, Boehm titration, TG-DTG, XRD and SEM-EDS techniques. The surfaces of all adsorbents clearly demonstrated negative charge (pH_pzc > pH of the mixture solution), resulting in a high adsorption capacity for each metal cation. Fe²⁺ was found to be more easily adsorbed on modified CP than the other kinds of metal cations. Synergistic effects between the carboxylic groups and MnO₂ on the surface of CPMn resulted in better performance for metal cation adsorption than was shown by CPHNO₃. The maximum adsorption capacities for Fe³⁺, Fe²⁺, Ca²⁺ and Zn²⁺ using CPMn, which were obtained from a monolayer adsorption process via Langmuir isotherms (R² > 0.99), were 70.67, 68.60, 5.06 and 22.38 mg g⁻¹, respectively. The adsorption behavior and monolayer-physisorption behavior, via a rapid adsorption process as well as single-step intra-particle diffusion, were also verified and supported using Dubinin–Radushkevich, Redlich–Peterson and Toth isotherms, a pseudo-second-order kinetic model and the Weber–Morris model. Moreover, the thermodynamic results indicated that the adsorption process of metal cations onto the CPMn surface was endothermic and spontaneous in nature. This research is expected to provide a green way for the production of low-cost/efficient adsorbents and to help gain an understanding of the adsorption behavior/process for the selective removal of metal ions from wastewater pollution.

Manganese dioxide-modified green biochar exhibited excellent capacity for adsorption of Fe³⁺, Fe²⁺, Ca²⁺ and/or Zn²⁺.     

A luminescent Cd(ii) coordination polymer as a multi-responsive fluorescent sensor for Zn2+, Fe3+ and Cr2O72− in water with fluorescence enhancement or quenching

A luminescent Cd(ii) coordination polymer, namely {[Cd(btic)(phen)]·0.5H₂O}_n (CP-1) (H₂btic = 5-(2-benzothiazolyl)isophthalic acid, phen = 1,10-phenanthroline), was constructed through the mixed-ligand method under solvothermal conditions. CP-1 manifests a chain structure decorated with uncoordinated Lewis basic N and S donors. CP-1 exhibits high sensing towards Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions with fluorescence enhancement or quenching. CP-1 exhibited a fluorescence enhancement for Zn²⁺ ions through weak binding to S and N atoms, and a fluorescence quenching for Fe³⁺ and Cr₂O₇²⁻ ions by an energy transfer process. The binding constants were calculated as 1.812 × 10⁴ mol⁻¹ for Zn²⁺, 4.959 × 10⁴ mol⁻¹ for Fe³⁺ and 1.793 × 10⁴ mol⁻¹ for Cr₂O₇²⁻. This study shows CP-1 as a rare multi-responsive sensor material for the efficient detection of Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.

A luminescent Cd(ii) coordination polymer can act as a multi-responsive sensor for efficiently detecting Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.     

Human liver alpha-D-mannosidase activity

Three types of α-D-mannosidase activity have been found in normal human liver, acidic activity with a pH optimum of 4.25, neutral activity with a pH optimum of 6.5 and activity with an intermediate pH optimum of 5.5. The acidic activity is heat stable and can be separated into two peaks A and B on DEAE-cellulose. Under certain conditions peak A converts to peak B spontaneously with an increase in molecular weight and decrease in pI. In peaks A and B there is both activity which is inhibited by EDTA and Co²⁺ but activated by Zn²⁺ and activity which is unaffected by EDTA, Co²⁺ or Zn²⁺. The neutral activity, which is heat labile, is obtained as a single peak of activity by chromatography on DEAE-cellulose, gel filtration and isoelectric focusing. The activity with a pH optimum of 5.5, which is activated by Co²⁺ and heat stable has similar isoelectric and Chromatographie properties to the neutral activity. The significance of these multiple forms of α-d-mannosidase is discussed in relation to the genetic disorder, mannosidosis.     

Effect of metal lons on phospholipase C (Heat-Labile Hemolysin) fromPseudomonas aeruginosa

Phospholipase C (PLC; heat-labile hemolysin) was purified fromPseudomonas aeruginosa culture supernatants to near homogeneity by ion exchange chromatography. Some chelating reagents and divalent metal ions were examined for their effects on the purified PLC activity. EDTA, ECTA, ando-phenanthroline did not inhibit the enzyme activity top-nitrophenylphosphorylcholine (pNPPC) at concentrations below 10 mmol/L. Inclubation with Zn²⁺, Cu²⁺, Co²⁺ or Ni²⁺ caused a decrease in the enzyme activity. The activity of EDTA-treated PLC was most remarkably decreased in the presence of Zn²⁺, followed in descending order by Cu²⁺, Co²⁺ and Ni²⁺, while other metal ions (Mg²⁺, Ca²⁺, Ba²⁺, and Mn²⁺) did not significantly affect the enzyme activity using concentrations up to 10 mmol/L. Zn²⁺ competitively inhibited the enzyme activity against pNPPC, with a Ki value of 0.3 mmol/L. The hemolytic activity of PLC was also completely inhibited in the presence of 1 mmol/L Zn²⁺, and inactivation of the enzyme by Zn²⁺ was not reversed by concomtitant addition of other divalent metal ions. These results suggest that hemolytic PLC fromP. aeruginosa has a unique property in that there is no metal ion requirement for its activity.     

Characterization of Trypsin Like Protease from <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> (Hubner) and Its Potential Inhibitors

Helicoverpa armigera is the most devastating pest of important crops causing heavy yield losses. The larval midgut harbours proteases and their inhibition starves insects to death or may disrupt their normal metabolism. So there is need to characterize gut protease and its potential inhibitors. A serine protease (trypsin like) from H. armigera gut was purified ~37 folds with 22 % yield and its molecular weight was found to be ~18.8 kilo Dalton. The Michaelis constant using N-α-benzoyl-DL-arginine-p-nitroanilide as a substrate was 0.31 mM. Maximum reaction rate was determined to be 3.47 nmol p-nitroaniline/min. Free energy of binding was found to be ?20.8 kJ/mol. The optimum temperature of enzyme was found to be 50 °C and around 17 % activity was maintained on heating at 80 °C for 30 min. The optimum pH for trypsin like activity was 11 with wide range of activity between 9 and 12 indicating that midgut digestive trypsin of H. armigera is active over wide range of alkaline pH. Metal ions Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺ were found to have the potential to inhibit the enzyme. Maximum inhibition was observed with Cu²⁺ (73 %) and minimum inhibition with Cd²⁺ (47 %). Copper inhibited trypsin non-competitively and zinc inhibited uncompetitively. Ascorbic acid, EDTA, leupeptin and benzamidine were found to be competitive inhibitors of H. armigera gut protease. The K_i values for Cu²⁺, ascorbic acid, EDTA, leupeptin and benzamidine were found to be 1.32, 38.23, 2.51 mM, 37.13 µM and 5.66 mM respectively.     

Optimization of ultrasonic-assisted extraction of pigment from Dioscorea cirrhosa by response surface methodology and evaluation of its stability

Response surface methodology (RSM) was utilized to optimize the ultrasonic-assisted extraction (UAE) of Dioscorea cirrhosa pigment (DCP). The results demonstrated that the yield of DCP is the highest (32.27%) when acetone volume fraction is 74%, extraction time is 31 min, and the temperature is 54 °C. Next, the effects of pH, temperature, light, metal ions, reductants and oxidants on the stability of DCP were further evaluated to confirm the best storage conditions of DCP. The results showed that DCP should be stored at a wide pH range of 3 to 9, below 80 °C and away from light. Metal ions such as Fe²⁺, Fe³⁺, and Ti⁴⁺ can destabilize DCP, while K⁺, Al³⁺, Ca²⁺, Cu²⁺, Mg²⁺, and Zn²⁺ have little impact on DCP. Moreover, DCP showed good anti-reduction and poor anti-oxidization properties. These results might provide the basic data and theoretical guidance for the application of DCP.

Response surface methodology (RSM) was utilized to optimize the ultrasonic-assisted extraction (UAE) of Dioscorea cirrhosa pigment (DCP).     

Studies on structure-function relationships of acetolactate decarboxylase from Enterobacter cloacae

Acetoin is an important bio-based platform chemical with wide applications. Among all bacterial strains, Enterobacter cloacae is a well-known acetoin producer via α-acetolactate decarboxylase (ALDC), which converts α-acetolactate into acetoin and is identified as the key enzyme in the biosynthetic pathway of acetoin. In this work, the enzyme properties of Enterobacter cloacae ALDC (E.c.-ALDC) were characterized, revealing a K_m value of 12.19 mM and a k_cat value of 0.96 s⁻¹. Meanwhile, the optimum pH of E.c.-ALDC was 6.5, and the activity of E.c.-ALDC was activated by Mn²⁺, Ba²⁺, Mg²⁺, Zn²⁺ and Ca²⁺, while Cu²⁺ and Fe²⁺ significantly inhibited ALDC activity. More importantly, we solved and reported the first crystal structure of E.c.-ALDC at 2.4 Å resolution. The active centre consists of a zinc ion coordinated by highly conserved histidines (199, 201 and 212) and glutamates (70 and 259). However, the conserved Arg150 in E.c.-ALDC orients away from the zinc ion in the active centre of the molecule, losing contact with the zinc ion. Molecular docking of the two enantiomers of α-acetolactate, (R)-acetolactate and (S)-acetolactate allows us to further investigate the interaction networks of E.c.-ALDC with the unique conformation of Arg150. In the models, no direct contacts are observed between Arg150 and the substrates, which is unlikely to maintain the stabilization function of Arg150 in the catalytic reaction. The structure of E.c.-ALDC provides valuable information about its function, allowing a deeper understanding of the catalytic mechanism of ALDCs.

Arg150 in E.c.-ALDC exhibited a unique tilted conformation implying the lower activities of E.c.-ALDC comparing to other bacterial ALDCs. Sequence conservation of E.c.-ALDC is represented by ribbons and lines (conserved, magenta to variable, cyan).     

Structural designing of Zn2SiO4:Mn nanocrystals by co-doping of alkali metal ions in mesoporous silica channels for enhanced emission efficiency with short decay time

High purity Zn₂SiO₄:Mn crystals were synthesized by impregnating a precursor solution into mesoporous silica followed by sintering process. The effects of doping alkali metal ions (Li⁺, Na⁺, K⁺) on the structural, morphological and photoluminescence properties were investigated. Formation of single phase α-Zn₂SiO₄:Mn crystals was confirmed from X-ray diffraction. The crystal size was significantly decreased from 54 nm to 35 nm with increasing molar concentration of alkali metal ion dopants in Zn₂SiO₄:Mn. Zn₂SiO₄:Mn crystals co-doped with alkali metal ions showed stronger emission and faster decay times compared to the un-doped Zn₂SiO₄:Mn phosphor. The highest emission quantum yields (EQEs) of 68.3% at λ_exc 254 and 3.8% at λ_exc 425 nm were obtained for the K⁺ ion doped samples with Mn²⁺ : K⁺ ratio of ∼1 : 1. With alkali metal ions (Li⁺, Na⁺, K⁺) co-doping, the decay time of Zn₂SiO₄:Mn crystals was shortened to ∼4 ms, whereas the emission intensity was elevated, with respect to un-doped Zn₂SiO₄:Mn crystals. Zn₂SiO₄:Mn crystal growth in silica pores together with selective doping with alkali metal ions paves a way forward to shorten the phosphor response time, without compromising emission efficiency.

Alkali metal ions co-doped Zn₂SiO₄:Mn nanocrystals were synthesized in a mesoporous silica matrix using solution impregnation method. A high PL-QY of 68.3% at λ_exc 254 nm and 3.8% at λ_exc 425 nm with faster decay time of <5 ms is obtained.     

Impact of metallic trace elements on relaxivities of iron-oxide contrast agents

In this work, well-defined 3 nm-sized Ca²⁺, Fe³⁺, Na⁺, Mg²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Cd²⁺ cation-adsorbed Fe₃O₄/γ-Fe₂O₃ nanoparticles were used as prototype systems to investigate the influence of metallic trace elements in body fluids on the relaxivities of iron-oxide contrast agents. It was found that surface-adsorbed cations formed a deterioration layer to induce pronounced relaxivity loss. Theoretical study showed that such relaxivity loss can be well described by a modified GCAS function, taking into account the harmonic cation oscillations around Fe₃O₄/γ-Fe₂O₃ nanoparticles. Quantum mechanics analyses revealed that even-parity and odd-parity states of harmonic oscillations are dominant in r₁ and r₂ relaxivities, respectively. Moreover, the harmonic oscillations of Na⁺ and Mg²⁺ cations around Fe₃O₄/γ-Fe₂O₃ nanoparticles are found to be classical forbidden, which are quite different from their counterparts located in the classical permissive area.

Distribution of relaxivity loss can be well described by a modified GCAS function.     

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.     

Highly active postspinel-structured catalysts for oxygen evolution reaction

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaBO₃ and spinel oxides ZnB₂O₄. Electrochemical impedance spectroscopy reveals that the higher OER activities for CaB₂O₄ series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.

Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited systematically higher catalytic activities in the oxygen evolution reaction (OER) than nominally conventional counterparts of perovskite LaBO₃ and spinel ZnB₂O₄.     

Novel magnetically separable anhydride-functionalized Fe3O4@SiO2@PEI-NTDA nanoparticles as effective adsorbents: synthesis,stability and recyclable adsorption performance for heavy metal ions

In this paper, a novel adsorbent, Fe₃O₄@SiO₂@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe₃O₄@SiO₂ nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe₃O₄@SiO₂@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe₃O₄@SiO₂, which showed a homogenous core–shell structure with three layers of about 300 nm diameter (Fe₃O₄ core: 200 nm, nSiO₂ layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe₃O₄@SiO₂@PEI-NTDA NPs was evaluated for single Pb²⁺ and coexisting Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb²⁺ removal through electrostatic interactions and chelation; Fe₃O₄@SiO₂@PEI-NTDA NPs exhibited preferable removal of Pb²⁺ with maximum adsorption capacity of 285.3 mg g⁻¹ for Pb²⁺ at a solution pH of 6.0, adsorbent dosage of 0.5 g L⁻¹, initial Pb²⁺ concentration of 200 mg L⁻¹ and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe₃O₄@SiO₂@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g⁻¹. The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe₃O₄@SiO₂@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb²⁺ in wastewater treatment.

A magnetically separable adsorbent, anhydride-functionalized Fe₃O₄@SiO₂@PEI-NTDA, was successfully constructed for removal of heavy metal ions from aqueous solution.     

Substrates for the assay of α-l-iduronidase

Procedures are described for the preparation of two disaccharides, 4-O -α -L-iduronosyl-2, 5-anhydro[³H]mannitol and $\text{3-O-α-}\text{l}\text{-iduronosyl}\text{-2,5--}\text{anhydro}\text{[}{}^3\text{H]-talitol}$, from heparin and dermatan sulfate, respectively. These disaccharides lend themselves to an easy assay of α-L-iduronidase which is based on the fractionation of the liberated neutral anhydro[³H]mannitol or anhydro[³H]talitol from the unreacted substrate by adsorption of the latter to Dowex 1.Investigation of the reaction conditions showed that the α-L-iduronidase activity (enzyme from human fibroblasts and Helix pomatia) was optimal at pH 3.6 in acetate buffer containing 0.01 M NaCl with iduronosyl-2,5-anhydro[³H]mannitol as substrate. For iduronosyl-2,5-anhydro[³H]talitol the pH optimum was 4.0 with the H. pomatia enzyme.The K_m for iduronosyl-2,5-anhydro[³H]mannitol was 0.23 mM with human fibroblasts and 0.04 mM with Helix enzyme; a KM value of 0.02 mM was determined for iduronosyl-2,5-anhydro[³H]talitol with the Helix α-l-iduronidase.     

GSH-doped GQDs using citric acid rich-lime oil extract for highly selective and sensitive determination and discrimination of Fe3+ and Fe2+ in the presence of H2O2 by a fluorescence “turn-off” sensor

Synthesis and characterization of graphene quantum dots (GQDs) simultaneously doped with 1% glutathione (GSH-GQDs) by pyrolysis using citric acid rich-lime oil extract as a starting material. The excitation wavelength (λ_max = 337 nm) of the obtained GSH-GQD solution is blue shifted from that of bare GQDs (λ_max = 345 nm), with the same emission wavelength (λ_max = 430 nm) indicating differences in the desired N and S matrices decorating the carbon based nanoparticles, without any background effect of both ionic strength and masking agent. For highly Fe³⁺-sensitive detection under optimum conditions, acetate buffer at pH 4.0 in the presence of 50 μM H₂O₂, the linearity range was 1.0–150 μM (R² = 0.9984), giving its calibration curve: y = 34.934x + 169.61. The LOD and LOQ were found to be 0.10 and 0.34 μM, respectively. The method’s precisions expressed in terms of RSDs for repeatability (n = 3 × 3 for intra-day analysis) were 2.03 and 3.17% and for reproducibility (n = 5 × 3 for inter-day analysis) were 3.11 and 4.55% for Fe²⁺ and Fe³⁺, respectively. The recoveries of the method expressed as the mean percentage (n = 3) were found in the ranges of 100.1–104.1 and 98.08–102.7% for Fe²⁺ and Fe³⁺, respectively. The proposed method was then implemented satisfactorily for trace determination of iron speciation in drinking water.

Synthesis and characterization of graphene quantum dots (GQDs) simultaneously doped with 1% glutathione (GSH-GQDs) by pyrolysis using citric acid rich-lime oil extract as a starting material.     

A novel boronic acid-based fluorescent sensor for selectively recognizing Fe3+ ion in real time

Boronic acid provides faster fluorescence response to Fe³⁺ compared to other reported sensors, which is critical for continuous dynamic detection. Herein, we reported a novel boronic acid-based sensor 4 that could recognize Fe³⁺ ion in real time. After 10 equiv. of Fe³⁺ ion (1 mM) was added, the fluorescence of sensor 4 was immediately quenched by 96%. While other ions, including Ba²⁺, Ca²⁺, Cr²⁺, Cd²⁺, Co²⁺, Cs²⁺, Cu²⁺, Fe²⁺, K⁺, Li⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺ or Zn²⁺, respectively, did not change the fluorescence significantly. Further tests indicated that the high selectively sensing Fe³⁺ ion benefits from the two boronic acid functionalities in the structure. Moreover, interference experiments showed this sensor has an excellent anti-interference ability. In addition, we performed binding activity test in rabbit plasma and other real samples for practical applications, obtaining similar results. And the thin layer loading sensor 4 was also successfully applied to recognize Fe³⁺ ion among various ions. Therefore, 4 may serve as a potential sensor for continuous monitoring and detecting Fe³⁺ ion in real time.

Boronic acid provides faster fluorescence response to Fe³⁺ compared to other reported sensors, which is critical for continuous dynamic detection.     

Study of the preparation of Maifan stone and SRB immobilized particles and their effect on treatment of acid mine drainage

The problems of acid mine drainage (AMD) in coal mine acidic wastewaters arise from a range of sources, including severe pollution with heavy metals and SO₄²⁻ and difficulties during treatment. Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO₄²⁻ by sulfate-reducing bacteria (SRB), Maifan stone–sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques using Shandong Maifan stone as the experimental material. A single factor experiment was used to investigate the influences of the dosage of Maifan stone, the particle size of Maifan stone and the dosage of SRB on the pH improvement effect and the removal rates of SO₄²⁻, Fe²⁺ and Mn²⁺. The Box–Behnken response surface method was used to determine the optimal preparation conditions for the Maifan stone and SRB immobilized particles in accordance with the ion removal rate and pH improvement effect when dealing with AMD. The results show that: (1) the optimal preparation conditions for Maifan stone synergistic SRB immobilized particles are determined by single factor experiment: the dosage of Maifan stone is 5 g, the particle size of Maifan stone is 0.075–0.106 mm, and the dosage of SRB is 25 mL per 100 mL; the removal rates of SO₄²⁻, Fe²⁺ and Mn²⁺ from AMD by the Maifan stone and SRB immobilized particles prepared under these conditions were 92.22%, 95.41% and 86.05%, and the pH was increased from 4.08 to 7.45. (2) From the variance analysis of the response surface model, it can be seen that the model effectively predicts the SO₄²⁻ removal rate, Fe²⁺ removal rate, Mn²⁺ removal rate and pH change. (3) After further optimization using the response surface method, the optimal preparation conditions of Maifan stone and SRB immobilized particles are determined as follows: Maifan stone dosage is 5 g, Maifan stone particle size is 0.075–0.106 mm, and SRB dosage is 25 mL per 100 mL. Through experiments, the removal rates of SO₄²⁻, Fe²⁺ and Mn²⁺ from AMD by the Maifan stone and SRB immobilized particles prepared under these conditions were 92.12%, 95.93% and 87.14%, respectively, and the pH was increased from 4.08 to 7.49.

Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO₄²⁻ by sulfate-reducing bacteria (SRB), Maifan stone–sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques.     

Hollow terbium metal–organic-framework spheres: preparation and their performance in Fe3+ detection

Hollow metal–organic framework (MOF) micro/nanostructures have been attracting a great amount of research interest in recent years. However, the synthesis of hollow metal–organic frameworks (MOFs) is a great challenge. In this paper, by using 1,3,5-benzenetricarboxylic acid (H₃BTC) as the organic ligand and 2,5-thiophenedicarboxylic acid (H₂TDC) as the competitive ligand and protective agent, hollow terbium MOFs (Tb-MOFs) spheres were synthesized by a one-pot solvothermal method. By comparing the morphology of Tb-MOFs in the presence and absence of H₂TDC, it is found that H₂TDC plays a key role in the formation of the hollow spherical structure. Single crystal analyses and element analysis confirm that H₂TDC is not involved in the coordination with Tb³⁺. Interestingly, Tb-MOFs can be used as the luminescent probes for Fe³⁺ recognition in aqueous and N,N-dimethylformamide (DMF) solutions. In aqueous solution, the quenching constant (K_SV) is 5.8 × 10⁻⁴ M⁻¹, and the limit of detection (LOD) is 2.05 μM. In DMF, the K_SV and LOD are 9.5 × 10⁻⁴ M⁻¹ and 0.80 μM, respectively. The sensing mechanism is that the excitation energy absorption of Fe³⁺ ions reduces the energy transfer efficiency from the ligand to Tb³⁺ ions.

(a) Pictures of Tb-MOFs suspension (left) and Fe³⁺ (right) under 365 nm illumination. (b) Pictures of Fe³⁺ with (left) and without (right) Tb-MOFs. (c) Pictures of Tb-MOFs powder before (left) and after (right) Fe³⁺ adsorption.     

Enhancing the sensitivity of a surface plasmon resonance-based optical sensor for zinc ion detection by the modification of a gold thin film

Surface plasmon resonance (SPR) sensors as novel optical sensors for the detection of a variety of analytes have been receiving increasing attention and their sensitivity has become the research hotspot recently. In this study, the sensitivity of an SPR optical sensor was enhanced by modifying a gold thin film with a nanocrystalline cellulose (NCC)-based material for zinc ion (Zn²⁺) detection that exists in the environment due to industrial processing. By replacing the gold thin film with a novel modified-gold thin film, Zn²⁺ can be detected from the range of 0 to 10 ppm using SPR. It is believed that the Zn²⁺ may interact with the negative charge molecules that exist on the modified-gold thin film, and this was confirmed via X-ray photoelectron spectroscopy (XPS). Moreover, this modified-gold-SPR has a high sensitivity of 1.892° ppm⁻¹ up to 0.1 ppm with an enhanced detection of Zn²⁺ as low as 0.01 ppm. The SPR results also followed the Langmuir isotherm model with a binding affinity of 1.927 × 10³ M⁻¹, which further confirmed the sensitivity of the SPR sensor. In addition, using the modified-gold thin film, SPR has a higher affinity towards Zn²⁺ compared to other metal ions, i.e. Ni²⁺, Fe²⁺, Cr²⁺, Mn²⁺, and Co²⁺.

This work focus on sensitivity enhancement of surface plasmon resonance (SPR) optical sensor by modifying the gold thin film with nanocrystalline cellulose (NCC) based material for zinc ion (Zn²⁺) detection.