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Environmentally benign methods for gold recovery and detection are highly desirable for a sustainable future. Herein, we demonstrate a selective recovery and detection strategy of gold with cucurbit[n]urils (Q[n= 5–7]) by means of outer-surface interactions. Tetrachloroaurate anion ([AuCl4]−) is able to be rapidly precipitated with Q[n] in forms of supramolecular adducts. X-ray crystallography of four Q[n= 5–7]·[AuCl4]−complexes reveal that strong outer-surface interactions between Q[n= 5–7] and [AuCl4]−are the major driving force for the formation of Q[n= 5–7]·[AuCl4]−complexes. Impressively, each Q[6] macrocycle is surrounded by 12 [AuCl4]−anions. Each of these 12 [AuCl4]−anions is connected to four adjacent [AuCl4]−anions, leading to the formation of a three-dimensional supramolecular framework with tubular channels. In addition, we found an interesting inclusion complex [Au(OH2)4]3+⊂Q[7] in the Q[7]·[AuCl4]−complex, which is the first example of hydrated metal cation encapsulated inside the cavity of Q[n]. Spectroscopic data suggest that Q[n= 5–7] possess a high affinity and selectivity for [AuCl4]−even in the presence of other transition-metal ions. Q[n] modified electrodes are found to be an effective material for the detection of trace gold in dilute solutions.

In this paper, a graphene modified glassy carbon electrode (GR-GCE), a carbon nanotube modified glassy carbon electrode (CNT-GCE), a carbon nanotube–graphene modified glassy carbon electrode (CNT–GR-GCE), and a gold nanoparticle–carbon nanotube–graphene modified glassy carbon electrode (GNP–CNT–GR-GCE) were prepared and characterized by FT-IR, atomic force microscopy (AFM), and electrochemical methods respectively. Electrogenerated chemiluminescence (ECL) of luminol was comparatively studied at these modified electrodes in neutral solution. The results revealed that carbon nanotube could intercalate into the graphene film and improve the conductivity of the CNT–GR composite significantly. The CNT–GR composite is an ideal matrix for the deposition of gold nanoparticles. At the GNP–CNT–GR-GCE, the effect of GR on luminol ECL is more predominant than that of CNT while the electrocatalytic effect of GNP on luminol ECL is well preserved. These nanomaterials exhibit a good synergic effect towards luminol ECL, which is more efficient than that of the sole material. The volume ratio of GR and CNT, the amount of modified suspension, the presence of N2and O2, and the supporting electrolytes could affect luminol ECL. Finally, the mechanisms of luminol ECL at the modified electrodes were proposed.

A simple and sensitive flow injection chemiluminescence (FI-CL) method for determination of the fungicide picoxystrobin was described for the first time. Picoxystrobin was injected into the mixed stream of luminol with KMnO4, and the CL signal of picoxystrobin could be greatly improved when an ultrasonic treatment was adopted. Meanwhile, the signal intensity increases with the analyte concentration proportionally. The effects of the ultrasonic conditions including ultrasonic frequency, time, power and temperature on the CL signal have been studied in detail. It was found that the higher the ultrasonic frequency used, the stronger the CL intensity increased. Since the variety of ultrasonic parameters can lead to the fluctuation of signal intensity, the CL mechanism was discussed. Under the optimized conditions, the CL intensity was linear for picoxystrobin concentration over the range of 2–150 ng mL−1with a 3σdetection limit of 0.27 ng mL−1. The relative standard deviation was 3.9% for 11 consecutive measurements of 20 ng mL−1picoxystrobin. The method was demonstrated by application to spiked water samples from different origins including river, ground and tap water.

It was found that chloroauric acid (HAuCl4) could be directly reduced by the luminescent reagent luminol in aqueous solution to form gold nanoparticles (AuNPs), the size of which depended on the amount of luminol. The morphology and surface state of as‐prepared AuNPs were characterized by transmission electron microscopy, UV/visible spectroscopy, X‐ray photoelectron spectroscopy, FTIR spectroscopy, and thermogravimetric analysis. All results indicated that residual luminol and its oxidation product 3‐aminophthalate coexisted on the surface of AuNPs through the weak covalent interaction between gold and nitrogen atoms in their amino groups. Subsequently, a luminol‐capped AuNP‐modified electrode was fabricated by the immobilization of AuNPs on a gold electrode by virtue of cysteine molecules and then immersion in a luminol solution. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The as‐prepared modified electrode exhibited an electrochemiluminescence (ECL) response in alkaline aqueous solution under a double‐step potential. H2O2was found to enhance the ECL. On this basis, an ECL sensor for the detection of H2O2was developed. The method is simple, fast, and reagent free. It is applicable to the determination of H2O2in the range of 3×10−7–1×10−3mol L−1with a detection limit of 1×10−7mol L−1(S/N=3).

The electrogenerated chemiluminescence (ECL) behavior of lucigenin in ethanol solution at a polycrystalline gold electrode was studied under conventional cyclic voltammetric conditions. Compared with the ECL of lucigenin in aqueous solution, one cathodic ECL peak (ECL‐1 at −0.98 V versus SCE) with a shoulder (S1at −0.42 V) and three new anodic ECL peaks (ECL‐2 at −0.53 V, ECL‐3 at 0.20 V, and ECL‐4 at 0.51 V) were observed, respectively, on the curve of ECL intensity versus potential. The effects of initial potential scan direction, the presence of O2or N2, potential scan ranges, supporting electrolyte and the concentration of lucigenin on these ECL peaks were examined. The electrochemistry of lucigenin in ethanol solution was also studied. The emitter of all ECL peaks was identified as N‐methylacridone (NMA) by analyzing the ECL spectra. The mechanism for these ECL peaks is proposed to be due to the reactions of lucigenin and its redox products such as Luc.+and DBA with dissolved oxygen or O2.−electrogenerated by the dissolved oxygen at different potentials. The formation of new anodic ECL peaks in ethanol solution is due to longer lifetime of superoxide ions and easier electro‐oxidation of DBA in nonaqueous solution, revealing that the solvent plays an important role in the lucigenin ECL reactions.

The electrogenerated chemiluminescence (ECL) behavior of lucigenin at a glassy carbon electrode in the presence of platinum nanoparticles dispersed in alkaline aqueous solutions was studied under conventional cyclic voltammetry (CV). Two ECL peaks were observed at -0.65 and -2.0 V (vsSCE), respectively. ECL-1 was a conventional ECL peak of lucigenin also observed in the absence of platinum nanoparticles. ECL-2 was a new ECL peak appearing in the hydrogen-evolution potential region. It was found that ECL-1 decreased and ECL-2 increased with an increase in the concentration of platinum nanoparticles. The ECL properties under various conditions were studied. It has been proposed that ECL-2 is likely due to that reductive intermediate HadsPt0formed during the hydrogen-evolution process that reduced lucigenin cation (Luc2) to monocation radial (Luc•); Luc•and HadsPt0reacted with dissolved oxygen to generate O2•-, which interacted with Luc•to produce the excited state N-methylacridone (NMA), giving rise to light emission at 495 nm. Pt nanoparticles synthesized in various methods showed different catalysis abilities for ECL-2. Furthermore, palladium particles similar to platinum particles can also catalyze the generation of ECL-2 while gold particles can not.

Graphene oxide (GO) and electrochemically reduced graphene (ERG) modified glassy carbon electrodes (GCE) were prepared and characterized by FT-IR, scanning electron microscopy (SEM), and electrochemical techniques, respectively. Electrogenerated chemiluminescence (ECL) of luminol was studied on the modified electrodes in neutral phosphate buffer solution (PBS). Either at the GO modified electrode or at the ERG modified electrode, the anodic ECL emission of luminol was inhibited greatly and only one cathodic ECL peak was obtained. The intensity of the cathodic ECL emission at the ERG modified electrode increased 123 times compared with that of the GO modified electrode or the bare electrode, which is due to the strong adsorption of dissolved oxygen by ERG film. Several impact factors of luminol ECL, such as the electrochemical reduction potential, the duration of the applied reduction potential, the pH values, the supporting electrolytes, and the potential scan rate were studied and the mechanism of the cathodic luminol ECL emission on the ERG modified electrode was proposed.