We report an interesting interaction between oxidized multiwalled carbon nanotubes (oxi-MWCNTs), tetra n-heptylammonium bromide (ionic liquid) and total chromium ((Cr(VI)/Cr(III)) in this study. The interaction between the IL and oxidized MWCNTs primarily involves electrostatic affinity between the quaternary ammonium cation, and surface carboxyl and hydroxyl groups in oxi-MWCNTs. The IL-oxi-MWCNT adsorbent acts as a host in welcoming the incoming guest hydrochromate anions and several interesting interactions such as cation–π interactions, electrostatic interactions as well as anion–π interactions could be conceptualized in this process. The abundant oxygen-containing functional groups on the surfaces of oxi-MWCNTs play an important role in Cr(VI)/Cr(III) sorption. Characterization of the adsorbent was performed using various characterization techniques such as cross polarization magic angle spinning nuclear magnetic resonance (¹³CPMAS-NMR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder-X-ray diffraction (Powder-XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy analysis (TEM), Brunauer–Emmett–Teller (BET) isotherm studies, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The capability of inductively coupled plasma mass spectrometry (ICP-MS) for Cr(VI) adsorption was extensively studied under different optimal parameters and the maximum adsorption capacity was found to be 85.83 mg g⁻¹ from a nonlinear Langmuir isotherm model. A kinetic study confirms a pseudo second order model and the process could be upgraded by column studies to a sample volume of 2000 mL. Effective regeneration of the adsorbent could be accomplished with sodium hydroxide and the potential of this novel adsorbent has been examined in the removal of Cr(VI)/Cr(III) from aqueous solutions.

We present a simple, one-pot approach for synthesizing ultrafine platinum (Pt) nanoclusters (NCs) under alkaline conditions using lysozyme (Lys) as a template. From the analysis of the nanoclusters by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, Lys VI-stabilized Pt NCs majorly consisted of Pt₄ clusters. The formation of Pt NCs was confirmed using X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy. The maximal fluorescence of Pt NCs appears at 434 nm with a quantum yield of 0.08, a fluorescence lifetime of 3.0 ns, and excitation-dependent emission wavelength behavior. Pt NCs exhibit an intrinsic oxidase-like activity because Pt NCs can catalyze O₂ oxidation of organic substrates through a four-electron reduction process. Compared with larger Pt nanoparticles, the Pt NCs produce substantially greater catalytic activity in the O₂-mediated oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), 3,3′,5,5′-tetramethylbenzidine, and dopamine.

This study describes the synthesis of fluorescent polydopamine dots (PDs) through hydroxyl radical-induced degradation of polydopamine nanoparticles. The decomposition of polydopamine nanoparticles to fluorescent PDs was confirmed using transmission electron microscopy and dark-field microscopy. The analysis of PDs by using laser desorption/ionization time-of-flight mass spectrometry revealed that the PDs consisted of dopamine, 5,6-dihydroxyindole, and trihydroxyindole units. Oligomerization and self-assembly of these units produced a broad adsorption band, resulting in an excitation-wavelength-dependent emission behavior. The maximal fluorescence of PDs appeared at 440 nm with a quantum yield of 1.2%. The coordination between the catechol groups of PDs and ferric ions (Fe³⁺) quenched the fluorescence of PDs; the limit of detection at a signal-to-noise ratio of 3 for Fe³⁺ was determined to be 0.3 μM. The presence of pyrophosphate switched on the fluorescence of the PD–Fe³⁺ complexes. Compared to the other reported methods for sensing Fe³⁺, PDs provided simple, low-cost, and reusable detection of Fe³⁺.

We developed a new homogeneous assay—using SYBR Green I and repeats of 20 C nucleotides—for the highly selective and sensitive detection of silver ions and silver nanoparticles.