Novel functional fiber loaded with carbon dots for the deep removal of Cr(VI) by adsorption and photocatalytic reduction

Synthesis and characterization of PANI-ZrWPO4 nanocomposite: adsorption-reduction efficiency and regeneration potential for Cr(VI) removal

A novel polyaniline zirconium tungstophosphate (PANI-ZrWPO4) nanocomposite was successfully synthesized through an in situ oxidative polymerization reaction followed by a microwave irradiation process. The synthesized nanocomposite was characterized by using FESEM, EDX, TEM, XRD, FTIR, Raman, TGA-DTA, XPS, and N2 adsorption-desorption analysis and chemical analysis to know about the formation of material. The results of the FTIR and Raman spectra confirmed that the conducting PANI polymer interacted with ZrWPO4 to form the PANI-ZrWPO4 nanocomposite. The XRD data showed that the composite had a crystalline nature. The TEM and FESEM images revealed that polyaniline had formed on the exterior of the PANI-ZrWPO4 nanocomposite. Further investigation was done on the efficiency of the PANI-ZrWPO4 nanocomposite as an adsorbent for Cr(VI) removal through batch adsorption experiments. The maximum Langmuir adsorption capacity of PANI-ZrWPO4 was found to be 71.4 mg g-1. The removal of Cr(VI) was optimized with the six variables namely adsorbent dose, initial concentration, Time, pH, Temperature, and stirring rate using the Box-Behnken design (BBD) model. The XPS spectra confirmed simultaneously adsorption reduction occurs Cr(VI) to Cr(III) through in situ chemical reduction. Moreover, the regeneration efficiency of PANI-ZrWPO4 was studied, and it was found to be able to remove around 80% of Cr(VI) even after five cycles, demonstrating its potential as an effective and reusable adsorbent.

Nanocellulose/carbon dots hydrogel as superior intensifier of ZnO/AgBr nanocomposite with adsorption and photocatalysis synergy for Cr(VI) removal

A novel nanocellulose/carbon dots hydrogel (NCH) was fabricated using cellulose nanofibrils (CN), carbon dots (CD) and zinc oxide (ZnO)/silver bromide (AgBr) nanocomposite, where CD enhanced amino group-induced adsorption of hexavalent chromium (Cr(VI)) and promoted the photocatalytic properties of ZnO/AgBr nanocomposite via the transfer of photogenerated electrons, resulting in enhanced efficiency in the removal of Cr(VI) from aqueous solution. The structure, morphology, and physicochemical properties of the prepared NCH were characterized, with the results of adsorption and photocatalysis experiments showing the maximum theoretical adsorption capacity of the NCH to be 315 mg/g, 219 times that of the ZnO/AgBr nanocomposite; the apparent removal rate constant of the NCH was 0.0319 min^-1, 11.7 times that of the ZnO/AgBr nanocomposite. Furthermore, the removal performance of NCH was attributed to CD-enhanced synergistic adsorption and photocatalysis effects, supported by characterization and experimental results. This work provides insight into the design and fabrication of a novel adsorptive photocatalyst with CD-enhanced synergistic adsorption and photocatalysis effects for removing Cr(VI) from aqueous solution.

Anchoring silver nanoparticles on nanofibers by thermal bonding to construct functional surface

Generally, the anchoring of inorganic nanoparticles onto the surface of fibers faces the problem of poor stability, which limits the wide application of nanoparticle functionalized fibers. Herein, nanofibers with shell-core structures were constructed by coaxial electrospinning of two polymers with different melting points (T_m). Polyglycolic acid (PGA, T_m = 225 °C) was employed as the core layer, while polycaprolactone (PCL, T_m = 60 °C) was used as the shell layer. Silver nanoparticles (AgNPs) were electrosprayed on the nanofibers and the shell layer (PCL) was heated and melted to bond the AgNPs, thus realizing a stable AgNP-composited nanofiber for the construction of antibacterial functional surface. By regulating the shell-core flow ratio and the condition for heat treatment, the appropriate thickness of the shell layer was obtained with a flow ratio of 3:1 (PCL:PGA). The optimal composite structure was constructed when the thermal bonding was taken under 80 °C for 5 min. Furthermore, it was found that the composite nanofibers prepared by thermal bonding had better hydrophilicity, mechanical property, and AgNPs bonding stability, and their antibacterial rate against Staphylococcus aureus (S. aureus) reached over 97%. Overall, a facile and universal method for the preparation of nanoparticle-anchored nanofibers was established in this study. The robust nanoparticle-composited nanofibers are promising for applications in optoelectronic devices, electrode materials, and so on.

One-pot hydrothermal preparation of manganese-doped carbon microspheres for effective deep removal of hexavalent chromium from wastewater

Mn-doped activated carbon microspheres (MnO_x/ACS) with super-high adsorption capacities and deep removal capability for hexavalent chromium (Cr(VI)) were successfully prepared via an ammonium persulfate-assisted hydrothermal method followed by potassium oxalate activation using KMnO₄ and sucrose as raw materials. Their -physical and chemical properties, as well as those of Mn-doped non-activated carbon spheres (MnO_x/CS), were characterized by XRD, SEM, TEM, EDS-mapping, XPS, N₂ adsorption-desorption, ICP-AES, and elemental analysis. It was found that the manganese oxide (MnO_x) particles were uniformly embedded within the carbon spheres via layer-by-layer capture, and the MnO_x/ACS exhibited strong redox activity because of the multivalent nature of MnO_x, resulting in excellent adsorption performance via reduction. In particular, MnO_x/ACS-4 with a Mn content of 1.06 wt% and a specific surface area of 1405.7 m² g^-1 achieved a maximum adsorption capacity of 660.7 mg g^-1; this can reduce Cr(VI) content to less than 0.05 mg L^-1, which meets the corresponding Chinese drinking water quality standard when the initial concentration of Cr(VI) is less than 400 mg L^-1. Furthermore, this highly efficient method can be extended to prepare V-, Mo-, or W-doped carbon microspheres with significantly enhanced adsorption performance for Cr(VI) compared to bare activated carbon sphere, indicating their good application prospect for the deep removal for heavy metal ions from wastewater.