RSC Advances

Zhang, Jinling; Jin, Xin; Zhao, Hui; Yang, Chaohe

doi: 10.1039/d1ra07814cpmid: 35425227

The sulfuric acid-based alkylation process, which leads the industrial application market, still struggles with effectively removing a large number of organic pollutants from hazardous spent sulfuric acid. A synergistic advanced oxidation process was constructed to degrade the organic pollutants with H2O2 and sodium persulfate as the synergistic oxidants and apricot shell-derived biochar (OBC) as the catalyst. Taking the total organic carbon (TOC) and the color scale as the indices, the effects of critical experimental factors, i.e., reaction temperature, initial oxidant concentration, catalyst dosage, and aeration rate, were optimized. The results showed that the removal rates of TOC and the color of the spent sulfuric acid reached ∼91% and 96.6%, respectively, after 150 min under the optimum conditions. Besides, the efficient and low-cost OBC catalyst developed in this study could be continuously used for at least four times with about 75% TOC removal and 80% color removal, exhibiting favorable stability and good resistance to acid corrosion. Further study confirmed that the SO4−˙ and ˙OH radicals generated in the synergistic advanced oxidation process strengthened the degradation and elimination of organic pollutants. The synergistic advanced oxidation process could provide a feasible insight for spent sulfuric acid treatment.

Mitsuya, Kengo; Goto, Satoru; Otsuka, Yuta; Kawano, Yayoi; Hanawa, Takehisa

doi: 10.1039/d1ra09086kpmid: 35425255

Polytetrafluoroethylene (PTFE) has excellent physical properties and has been used in a wide range of applications in various fields. Adsorption research on PTFE is essential as primary research for the further application of PTFE. We attempted to adsorb coal tar dyes and model drugs such as lidocaine onto PTFE as a guideline to search for medicines that adsorb onto PTFE. Saturation curves were obtained after analyzing the adsorption of coal tar dyes on PTFE using the Hanes–Woolf plot. In addition, we collected multiple cases of ATR-FTIR spectral changes and/or retention depending on TPM derivatives and other adsorbates. Lidocaine matched some coal tar dye for the apparent spectral changes between the adsorbed molecules and its crystalline powder. The apparent spectral changes are blue-shifted, suggesting a hydrophobic interaction between the dyes/lidocaine and porous PTFE. This work provides a promising strategy for further application of PTFE.

Li, Qiang; Hu, Yulan; Zhang, Bingjian

doi: 10.1039/d1ra09169gpmid: 35425254

With a view to preventing fungal deterioration of historical stone artworks, we report the use of phosphonium-based ionic liquids (ILs) as potent antifungal agents against dematiaceous fungi commonly found on heritage stones. Three ILs: tributyldodecylphosphonium polyoxometalate [P44412][POM], tributyltetradecylphosphonium polyoxometalate [P44414][POM], and trihexyltetradecylphosphonium polyoxometalate [P66614][POM] were prepared and their thermal stabilities and in vitro antifungal activities were evaluated. From the ramped temperature thermogravimetric analysis and antifungal experiments it can be clearly observed that the alkyl chain length of the tetraalkylphosponium cation has a significant influence on the thermal and antifungal properties. The thermal stability and antifungal activity decreased as the number of carbon atoms of the alkyl substituents increased and, thus, followed the order [P44412][POM] > [P44414][POM] > [P66614][POM]. In addition, inoculation of four fungal species on IL-coated sandstone surfaces showed significant inhibition of fungal growth, endowing the materials with potential applications in heritage sandstone conservation.

Rodríguez, Diego F.; Moglie, Yanina; Ramírez-Sarmiento, César A.; Singh, Sachin Kumar; Dua, Kamal; Zacconi, Flavia C.

doi: 10.1039/d1ra08053apmid: 35425264

The fields of click chemistry and biocatalysis have rapidly grown over the last two decades. The development of robust and active biocatalysts and the widespread use of straightforward click reactions led to significant interactions between these two fields. Therefore the name bio-click chemistry seems to be an accurate definition of chemoenzymatic reactions cooperating with click transformations. Bio-click chemistry can be understood as the approach towards molecules of high-value using a green and sustainable approach by exploiting the potential of biocatalytic enzyme activity combined with the reliable nature of click reactions. This review summarizes the principal bio-click chemistry reactions reported over the last two decades, with a special emphasis on small molecules. Contributions to the field of bio-click chemistry are manifold, but the synthesis of chiral molecules with applications in medicinal chemistry and sustainable syntheses will be especially highlighted.

Chen, Zhi; Zeng, Jun; Zhang, Zhi-Bo; Zhang, Zhi-Jie; Ma, Shan; Tang, Cong-Ming; Xu, Jun-Qiang

doi: 10.1039/d1ra08699epmid: 35425277

As a biomass resource, corncob is a kind of agricultural by-product with wide sources and low cost. Because its composition contains a large number of functional polymers such as cellulose, chitosan, and semi chitosan, corncob can be chemically modified to prepare a variety of adsorption materials. In this study, a magnetic gel material (PEI-CC@Fe3O4) consisting of corncob modified by glutaraldehyde-crosslinked polyethyleneimine (PEI) was successfully prepared and applied to the adsorption of heavy metal ions in aqueous solutions. The structure, thermal stability, and adsorption of heavy metal ions of the magnetic gel material (PEI-CC@Fe3O4) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction phase analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results showed that PEI was crosslinked to the corncob through Aldol reaction and Schiff-base reaction. The heavy metal ion adsorption experiment showed that the PEI-CC@Fe3O4 had better adsorption toward divalent copper ions and divalent lead ions at 303 K, and the maximum adsorption capacities reached 459.4 mg g−1 and 290.8 mg g−1, respectively. Moreover, the study of isothermal adsorption and adsorption kinetics shows that the adsorption process is pseudo-second-order kinetics model adsorption, which belongs to Langmuir isothermal adsorption. Such excellent adsorption performance will contribute to the application of corncob biomass materials in industrial polluted wastewater.

Kim, Kwang-Hyon; Kim, Il-Pong

doi: 10.1039/d1ra07858epmid: 35425274

For observing high-Q quasi-bound states in the continuum (BIC), the metasurfaces should be made of high-index materials, restricting their applications due to the limited material functionalities. In this work, we demonstrate that high-Q quasi-BIC can also be obtained by using lower-index dielectrics, provided that the metasurfaces are supported by metallic substrates. Strong field confinement assisted by plasmon excitation on the surface of metallic substrate enables realizing quasi-BIC even when using the lower-index materials such as zinc oxide. The numerical results show that high Q-factors in the order of several hundreds can be obtained with such metasurfaces of lower-index materials. They do not exhibit, however, quasi-BIC when supported by dielectric substrates due to the strong mode leakage originating from the low index contrast. Quite interestingly, metasurfaces made of high-index dielectrics supported by metallic substrates exhibit lower Q-factors compared with the metasurfaces of lower-index dielectrics due to the stronger penetration of mode field into the metallic substrate. The presented results can find important applications for photonic purposes, including efficient UV generation and low-threshold lasing from the lower-index dielectric metasurfaces.

Cong, Junhao; Xie, Xuehui; Liu, Yanbiao; Qin, Yan; Fan, Jiao; Fang, Yingrong; Liu, Na; Zhang, Qingyun; Song, Xinshan; Sand, Wolfgang

doi: 10.1039/d1ra08090cpmid: 35425265

One of the main mechanisms of bacterial decolorization and degradation of azo dyes is the use of biological enzymes to catalyze the breaking of azo bonds. This paper shows the expression and properties of a novel azo reductase (hybrid-cluster NAD(P)-dependent oxidoreductase, accession no. A0A1S1BVU5, named BVU5) from the bacterial flora DDMZ1 for degradation of azo dyes. The molecular weight of BVU5 is about 40.1 kDa, and it contains the prosthetic group flavin mononucleotide (FMN). It has the decolorization ability of 80.1 ± 2.5% within 3 min for a dye concentration of 20 mg L−1, and 53.5 ± 1.8% even for a dye concentration of 200 mg L−1 after 30 min. The optimum temperature of enzyme BVU5 is 30 °C and the optimum pH is 6. It is insensitive to salt concentration up to a salinity level of 10%. Furthermore, enzyme BVU5 has good tolerance toward some metal ions (2 mM) such as Mn2+, Ca2+, Mg2+ and Cu2+ and some organic solvents (20%) such as DMSO, methanol, isopentyl, ethylene glycol and N-hexane. However, the enzyme BVU5 has a low tolerance to high concentrations of denaturants. In particular, it is sensitive to the denaturants guanidine hydrochloride (GdmCl) (2 M) and urea (2 M). Analysis of the dye substrate specificity shows that enzyme BVU5 decolorizes most azo dyes, which is indicating that the enzyme is not strictly substrate specific, it is a functional enzyme for breaking the azo structure. Liquid chromatography/time-of-flight/mass spectrometry (LC-TOF-MS) revealed after the action of enzyme BVU5 that some intermediate products with relatively large molecular weights were produced; this illustrates a symmetric or an asymmetric rapid cleavage of the azo bonds by this enzyme. The potential degradation pathways and the enzyme-catalyzed degradation mechanism are deduced in the end of this paper. The results give insight into the potential of a rapid bio-pretreatment by enzyme BVU5 for processing azo dye wastewater.

Alrawashdeh, Lubna; Assaf, Khaleel I.; Alshaer, Walhan; Odeh, Fadwa; Bani-Atta, Suhair A.

doi: 10.1039/d1ra08460gpmid: 35425234

In this study, the formation of a host–guest inclusion complex between cucurbit[7]uril (CB[7]) and thymoquinone (TQ) was investigated in aqueous solution. The formation of a stable inclusion complex, CB[7]–TQ, was confirmed by using different techniques, such as 1H NMR and UV-visible spectroscopy. The aqueous solubility of TQ was clearly enhanced upon the addition of CB[7], which provided an initial indication for supramolecular complexation. The complexation stoichiometry and the binding constant of the inclusion complex were determined through a combination of two sets of titration methods, including UV-visible and fluorescence displacement titrations. Both methods suggested the formation of a 1 : 1 stoichiometry between CB[7] and TQ with moderate binding affinity of 3 × 103 M−1. Density functional theory (DFT) calculations were also performed to verify the structure of the resulted host–guest complex and to support the complexation stoichiometry. The theoretical calculations were in agreement with experimental results obtained by 1H NMR spectroscopy. Most importantly, the cytotoxic effect of the CB[7]–TQ complex was investigated against cancer and normal cell lines. The results showed that the anticancer activity of TQ against MDA-MB-231 cells was enhanced by the complexation with CB[7], while no significant effect was observed in MCF-7 cells. The results also confirmed the low toxicity of the CB[7] host molecule that supports the use of CB[7] as a drug carrier.

Qi, Haiyan; Sun, Xiaona; Jing, Tao; Li, Jinlong; Li, Jun

doi: 10.1039/d1ra08890dpmid: 35425249

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg2+ and glutathione (GSH). This was attributed to Hg2+ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg2+ and the sulfhydryl of GSH. Based on the “on-off-on” tactic, the detection limits of Hg2+ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg2+ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

Cuc, Nguyen Thi Thanh; An, Nguyen Truong; Ngan, Vu Thi; Chandra, Asit. K.; Trung, Nguyen Tien

doi: 10.1039/d1ra07444jpmid: 35425273

Geometrical structure, stability and cooperativity, and contribution of hydrogen bonds to the stability of complexes between chalcogenoaldehydes and water were thoroughly investigated using quantum chemical methods. The stability of the complexes increases significantly when one or more H2O molecules are added to the binary system, whereas it decreases sharply going from O to S, Se, or Te substitution. The O–H⋯O H-bond is twice as stable as Csp2–H⋯O and O–H⋯S/Se/Te H-bonds. It is found that a considerable blue-shift of Csp2–H stretching frequency in the Csp2–H⋯O H-bond is mainly determined by an addition of water into the complexes along with the low polarity of the Csp2–H covalent bond in formaldehyde and acetaldehyde. The Csp2–H stretching frequency shift as a function of net second hyperconjugative energy for the σ*(Csp2–H) antibonding orbital is observed. Remarkably, a considerable Csp2–H blue shift of 109 cm−1 has been reported for the first time. Upon the addition of H2O into the binary systems, halogenated complexes witness a decreasing magnitude of the Csp2–H stretching frequency blue-shift in the Csp2–H⋯O H-bond, whereas CH3-substituted complexes experience the opposite trend.