Fe3O4-NPs/orange peel composite as magnetic heterogeneous Fenton-like catalyst towards high-efficiency degradation of methyl orange

Construction of a Dual-Functionalized Acid-Base Nanocatalyst via HEPES Buffer Functionalized on Fe3O4 as a Reusable Catalyst for Annulation Reactions

Herein, we present a highly efficient dual-functionalized acid-base nanocatalyst, denoted as Fe3O4@GLYMO-HEPES, featuring sulfuric acid and tertiary amines as its dual functional components. This catalyst is synthesized through the immobilization of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as the source of these functionalities onto magnetite (Fe3O4) using 3-glycidoxypropyltriethoxysilane (GLYMO) as a linker. Characterization studies confirm the integrity of the Fe3O4 core, with the GLYMO-HEPES coating exhibiting no phase changes. Furthermore, Fe3O4@GLYMO-HEPES nanoparticles demonstrate a uniform size distribution without aggregation. Notably, the catalyst exhibits remarkable stability up to 200 °C and possesses a saturation magnetization value of 31.5 emu/g, facilitating easy recovery via magnetic separation. These findings underscore the potential of Fe3O4@GLYMO-HEPES as a versatile and recyclable nanocatalyst for various applications. Its catalytic ability was evaluated in the synthesis of various pyrano[2,3-c]pyrazoles and 2-amino-3-cyano-4H-chromenes through a tandem Knorr-Knoevenagel-Michael-Thorpe-Ziegler-type heterocyclization mechanism, using different aldehydes. A wide range of fused heterocycles was synthesized having good to excellent yields. The process is cost-effective, safe, sustainable, and scalable, and the catalyst can be reused up to five times. The prepared catalyst was found to be highly stable and heterogeneous and showed good recyclability.

Insights into the pH-Dependent Adsorption Behavior of Ionic Dyes on Phosphoric Acid-Activated Biochar

Activated biochar is a promising porous carbonaceous adsorbent material for organic pollutant removal, but it remains challenging to obtain high porosity and aromaticity through a simple and low-cost synthetic method. The common adsorption mechanisms of organic dyes on activated biochar should be further investigated in order to guide the synthesis of high-efficiency adsorbent materials. Here, we proposed a high-yield (up to 40 wt %) synthetic method of phosphoric acid-activated biochar from pomelo peel (PPC) with a high specific area of 877.3 m²/g through a facile thermal treatment at a relatively low temperature (250 °C). The specific activation mechanism of H₃PO₄ in the preparation of the adsorbent was investigated by a range of experiments and characterizations. The kinetic and isotherm experiments are also conducted to evaluate its dye adsorption behavior. According to the adsorption experiment results, PPC exhibits high saturated adsorption capacities for methyl orange (MO, 239.1 mg/g), rhodamine B (RhB, 2821.8 mg/g), methylene blue (MB, 580.5 mg/g), and crystal violate (CV, 396.6 mg/g) according to the Langmuir model. The maximum initial concentration of each dye solution for acquiring 90% removal efficiency is estimated to be 234.55 ppm (MO), 2943.8 ppm (RhB), 633.8 ppm (MB), and 423.6 ppm (CV) at 298 K with an adsorbent dosage of 1 g/L. The characterization results also indicate PPC has a complex synergetic mechanism for ionic dye adsorption behavior. This provides perspectives regarding PPC as a promising biochar adsorbent from biomass waste, which is probably useful for high-efficiency dye removal in water treatment.

Biowaste- and nature-derived (nano)materials: Biosynthesis, stability and environmental applications

Due to the environmental pollution issues and the supply of drinking/clean water, removal of both inorganic and organic (particularly dyes, nitroarenes, and heavy metals) to non-dangerous products and useful compounds are very important transformations. The deployment of sustainable and eco-friendly nanomaterials with exceptional structural and unique features such as high efficiency and stability/recyclability, high surface/volume ratio, low-cost production routes has become a priority; nonetheless, numerous significant challenges/restrictions still remained unresolved. The immobilization of green synthesized metal nanoparticles (NPs) on the natural materials and biowaste generated templates have been analyzed widely as a greener approach due to their environmentally friendly preparation methods, earth-abundance, cost-effectiveness with low energy consumption, biocompatibility, as well as adjustability in various cases of biomolecules as bioreducing agents. Natural and biowaste materials are widely considered as important sources to fabricate greener and biosynthesized types of metal, metal oxide, and metal sulfide nanomaterials using plant extracts. Integrating green synthesized nanoparticles with various biotemplates offers new practical composites for mitigating environmental challenges. In this review, degradation of dyes, reduction of toxic nitrophenols, absorption of heavy metals, and other hazardous/toxic environmental pollutants from contaminated water bodies using biowaste- and nature-derived nanomaterials are highlighted.