Green synthesis of reusable super-paramagnetic diatomite for aqueous nickel (II) removal

Microalgae derived honeycomb structured mesoporous diatom biosilica for adsorption of malachite green: Process optimization and modeling

The present study investigated the removal of malachite green dye from aquifers by means of microalgae-derived mesoporous diatom biosilica. The various process variables (dye concentration, pH, and adsorbent dose) influencing the removal of the dye were optimized and their interactive effects on the removal efficiency were explored by response surface methodology. The pH of the solution (pH = 5.26) was found to be the most dominating among other tested variables. The Langmuir isotherm (R2 = 0.995) best fitted the equilibrium adsorption data with an adsorption capacity of 40.7 mg/g at 323 K and pseudo-second-order model (R2 = 0.983) best elucidated the rate of dye removal (10.6 mg/g). The underlying mechanism of adsorption was investigated by Weber-Morris and Boyd models and results revealed that the film diffusion governed the overall adsorption process. The theoretical investigations on the dye structure using DFT-based chemical reactivity descriptors indicated that malachite green cations are electrophilic, reactive and possess the ability to accept electrons, and are strongly adsorbed on the surface of diatom biosilica. Also, the Fukui function analysis proposed the favorable adsorption sites available on the adsorbent surface.

Octadecyl and sulfonyl modification of diatomite synergistically improved the immobilization efficiency of lipase and its application in the synthesis of pine sterol esters

Phytosterols usually have to be esterified to various phytosterol esters to avoid their disadvantages of unsatisfactory solubility and low bioavailability. The enzymatic synthesis of phytosterol esters in a solvent-free system has advantages in terms of environmental friendliness, sustainability, and selectivity. However, the limitation of the low stability and recyclability of the lipase in the solvent-free system, which often requires a relatively high temperature to induce the viscosity, also increased the industrial production cost. In this context, a low-cost material, namely diatomite, was employed as the support in the immobilization of Candida rugosa lipase (CRL) due to its multiple modification sites. The Fe3 O4 was also then introduced to this system for quick and simple separation via the magnetic field. Moreover, to further enhance the immobilization efficiency of diatomite, a modification strategy which involved the octadecyl and sulfonyl group for regulating the hydrophobicity and interaction between the support and lipase was successfully developed. The optimization of the ratio of the modifiers suggested that the -SO3 H/C18 (1:1.5) performed best with an enzyme loading and enzyme activity of 84.8 mg·g-1 and 54 U·g-1 , respectively. Compared with free CRL, the thermal and storage stability of CRL@OSMD was significantly improved, which lays the foundation for the catalytic synthesis of phytosterol esters in solvent-free systems. Fortunately, a yield of 95.0% was achieved after optimizing the reaction conditions, and a yield of 70.0% can still be maintained after six cycles.

Efficient Degradation of Sulfamethoxazole by Diatomite-Supported Hydroxyl-Modified UIO-66 Photocatalyst after Calcination

Sulfamethoxazole (SMX) is a widely used antibiotic to treat bacterial infections prevalent among humans and animals. SMX undergoes several transformation pathways in living organisms and external environments. Therefore, the development of efficient remediation methods for treating SMX and its metabolites is needed. We fabricated a photo-Fenton catalyst using an UIO-66 (Zr) metal-organic framework (MOF) dispersed in diatomite by a single-step solvothermal method for hydroxylation (HO-UIO-66). The HO-UIO-66-0/DE-assisted Fenton-like process degraded SMX with 94.7% efficiency; however, HO-UIO-66 (Zr) is not stable. We improved the stability of the catalyst by introducing a calcination step. The calcination temperature is critical to improving the catalytic efficiency of the composite (for example, designated as HO-UIO-66/DE-300 to denote hydroxylated UIO-66 dispersed in diatomite calcined at 300 °C). The degradation of SMX by HO-UIO-66/DE-300 was 93.8% in 120 min with 4 mmol/L H2O2 at pH 3 under visible light radiation. The O1s XPS signatures signify the stability of the catalyst after repeated use for SMX degradation. The electron spin resonance spectral data suggest the role of h+, •OH, •O2-, and 1O2 in SMX degradation routes. The HO-UIO-66/DE-300-assisted Fenton-like process shows potential in degrading pharmaceutical products present in water and wastewater.

Characterization of Chitosan-Hybridized Diatomite as Potential Delivery Systems of Oxaliplatin and 5-Fluorouracil Drugs: Equilibrium and Release Kinetics

The current work involves the modification of diatomite's biosiliceous frustules employing chitosan polymer chains (CS/Di) to serve as low-cost, biocompatible, multifunctional, and enhanced pharmaceutical delivery systems for 5-fluorouracil (5-Fu) together with oxaliplatin (OXPL). The CS/Di carrier displayed strong loading characteristics, notably at saturation (249.17 mg/g (OXPL) and 267.6 mg/g (5-Fu)), demonstrating a substantial 5-Fu affinity. The loading of the two types of medications onto CS/Di was conducted based on the kinetic behaviors of the conventional pseudo-first-order theory (R2 > 0.90). However, while the loading of OXPL follows the isotherm assumptions of the classic Langmuir model (R2 = 0.99), the loading of 5-Fu displays Fruendlich isotherm properties. Therefore, the 5-Fu loading displayed physical, heterogeneous, and multilayer loading properties, whereas the loading of OXPL occurred in homogeneous and monolayer form. The densities of occupied active sites of CS/Di were 37.19 and 32.8 mg/g for the sequestrations of OXPL and 5-Fu, respectively. Furthermore, by means of multimolecular processes, each loading site of CS/Di can bind up to 8 molecules of OXPL and 9 molecules of 5-Fu in a vertical orientation. This observation explains the higher loading capacities of 5-Fu in comparison to OXPL. The loading energies, which exhibit values <40 kJ/mol, provide confirmation of the dominant and significant consequences of physical processes as the regulating mechanisms. The release patterns of OXPL and 5-Fu demonstrate prolonged features over a duration of up to 120 h. The release kinetic simulation and diffusion exponents which are more than 0.45 provide evidence of the release of OXP and 5-Fu via non-Fickian transportation characteristics and the erosion/diffusion mechanism. The CS/Di carrier exhibited a substantial enhancement in the cytotoxicity of OXPL and 5-Fu against HCT-116 carcinoma cell lines, resulting in a reduction in cell viability by 4.61 and 2.26% respectively.

Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline ligands: Synthesis, properties and application as ion sensors

As we know, excessive metal ions can even damage human health. Herein, two novel kinds of fluorescent sensing materials Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline were synthesized and further applied to fluorescence detection for ions. The results show that Ni²⁺, Cu²⁺, and Pd²⁺ have excellent quenching effects on the fluorescence of Poly[9-(1,10-phenanthroline-2-yl)-9H-carbazol-3-amine] (PPNC), the LOD for these ions reaches 5.2 nM, 12.7 nM, 33.5 nM respectively. In the process of ion response, there is no shift of UV absorption peak, combined with IR spectra and theoretical calculation simulation, the quenching is considered to be caused by the coordination between metal ions and the second amine (-NH-) or 1,10-phenanthroline ligand of PPNC, which leads to the charge transfer from ligands to metal ions. In addition, an acid test was done for PPNC to verify and detect the presence of secondary amine (-NH-), and the results show that PPNC has good acid sensing ability which also supports the secondary amine (-NH-) structure. Finally, the paper test was performed on PPNC, indicating that PPNC has the potential for visual application.

High selective removal towards Hg(II) from aqueous solution with magnetic diatomite-based adsorbent functionalized by poly(3-aminothiophenol): conditional optimization, application, and mechanism

A novel diatomite-based (DMT) material was obtained by post-functionalization of DMT/CoFe₂O₄ with 3-aminothiophenol and applied to remove Hg(II) ions from aqueous solution. The obtained adsorbent of DMT/CoFe₂O₄-p-ATP was detected by various characterization means. The optimization of response surface methodology reveals that magnetic diatomite-based material of DMT/CoFe₂O₄-p-ATP has an optimal adsorption capability of 213.2 mg/g towards Hg(II). The removal process of Hg(II) is fitted well to pseudo-second-order and Langmuir models, respectively, indicating that the adsorption process is controlled by monolayer chemisorption. DMT/CoFe₂O₄-p-ATP exhibits superior affinity towards Hg(II) through electrostatic attraction and surface chelation, compared with other coexisting heavy metal ions. Meanwhile, the prepared adsorbent DMT/CoFe₂O₄-p-ATP displays excellent recyclability, good magnetic separation performance, and satisfying stability. The as-prepared diatomite-based DMT/CoFe₂O₄-p-ATP can be a promising adsorbent for mercury ions.

Selective adsorption of Hg(ii) with diatomite-based mesoporous materials functionalized by pyrrole-thiophene copolymers: condition optimization, application and mechanism

A novel diatomite-based mesoporous material of MCM-41/co-(PPy-Tp) was prepared with MCM-41 as carrier and functionalized with the copolymer of pyrrole and thiophene. The physicochemical characteristics of the as-prepared materials were characterized by various characterization means. The removal behaviour of Hg(ii) was adequately investigated via series of single factor experiments and some vital influence factors were optimized via response surface methodology method. The results exhibit that diatomite-based materials MCM-41/co-(PPy-Tp) has an optimal adsorption capability of 537.15 mg g-1 towards Hg(ii) at pH = 7.1. The removal process of Hg(ii) onto MCM-41/co-(PPy-Tp) is controlled by monolayer chemisorption based on the fitting results of pseudo-second-order kinetic and Langmuir models. In addition, the adsorption of Hg(ii) ions onto MCM-41/co-(PPy-Tp) is mainly completed through forming a stable complex with N or S atoms in MCM-41/co-(PPy-Tp) by electrostatic attraction and chelation. The as-developed MCM-41/co-(PPy-Tp) displays excellent recyclability and stabilization, has obviously selective adsorption for Hg(ii) in the treatment of actual electroplating wastewater. Diatomite-based mesoporous material functionalized by the copolymer of pyrrole and thiophene exhibits promising application prospect.

Mechanism underlying how a chitosan-based phosphorus adsorbent alleviates cadmium-induced oxidative stress in Bidens pilosa L. and its impact on soil microbial communities: A field study

In the present study, field experiments were conducted in Side village, Yangshuo, Guilin, Guangxi Province, China, using four C-BPA application levels (control (0 mg m^-2), T1 (100 mg m^-2), T2 (200 mg m^-2) and T3 (400 mg m^-2)) to clarify the mechanism by which a chitosan-based phosphorus adsorbent (C-BPA) applied as a passivator helps Bidens pilosa L. (B. pilosa L.) alleviate cadmium (Cd)-induced oxidative stress in Cd-contaminated soil. In the aqueous phase, C-BPA successfully adsorbed Cd²⁺ on the surface primarily via ion exchange, and C-BPA has potential Cd²⁺ adsorption capacity, enabling its use as a passivator in real Cd-contaminated environments. In Cd-contaminated soils, under C-BPA application at the T3 level, the pH value increased by 11.2%, and the acid-soluble form of Cd decreased by 26.5%. Additionally, the application of C-BPA improved the rhizosphere soil environment and impacted the soil microbial community diversity and structure. Among soil microbes, the soil fungal community was more sensitive than bacteria to C-BPA application. Dehydrogenase, acetic acid, soil pH and Eurotiomycetes or Dothideomycetes significantly impacted Cd accumulation in the leaves of B. pilosa L.; Cd accumulation in leaves was decreased by 68.1% under C-BPA application at the T3 level. Additionally, the variation of increased catalase (CAT) and peroxidase (POD) jointly promoted plant growth; the plant weight was increased by 112.7% under the C-BPA application at the T3 level. Notably, the production of CAT and POD by B. pilosa L. was more effective than the synthesis of glutathione (GSH) in helping B. pilosa L. eliminate excess reactive oxygen species (ROS). Therefore, our findings demonstrated that the application of C-BPA to Cd-contaminated soil can greatly improve the rhizosphere soil environment, help B. pilosa L. eliminate ROS and promote plant growth.