Solar Photocatalytic Phenol Polymerization and Hydrogen Generation for Flocculation of Wastewater Impurities

Abstract

Achieving global sustainability will require balancing encroaching climate changes while maintaining the existing quality of life. Using sunlight to purify wastewater while simultaneously generating usable fuels is an opportunity to approach both targets in a cost-efficient manner. In addition, converting biomass products to usable polymers is a sustainable approach for potentially replacing polystyrene or other petroleum-derived polymers. Phenols from medical, manufacturing, and agricultural waste are commonly found in many water sources, and they are known to foul common reverse osmosis membranes. Here, we show oxidative polymerization of guaiacol, an aromatic compound derived from biomass, with concurrent hydrogen gas generation by using platinum-seeded cadmium sulfide nanorods (Pt@CdS) as photocatalysts. Rather than forming short oligomers as typically made by enzymes such as laccase and peroxidase, the resulting polymers show higher molecular weights that can more easily flocculate out of water. By comparing guaiacol conversion to molecular weight and dispersity, we found the guaiacol to polymerize via a chain-growth process. We also show that Pt@CdS can polymerize other phenols as well by testing the monomers phenol, 2,6-dihydroxybenzoic acid, gallic acid, and vanillin. Lastly, because the aqueous solubility of these aromatic polymers decreases dramatically with molecular weight, polymerization reactions were also tested in biphasic solutions to determine whether chain growth could propagate in the oil phase. We show that the Pt@CdS nanoparticles can form stable Pickering emulsions in various biphasic combinations and that both H 2 formation and polymer molecular weight correlated to the partition coefficient of guaiacol into the oil phase as well as the solubility of the growing polymer chains. These combined studies demonstrate the possibility of using nanoscale photocatalysts to oxidatively polymerize phenolic substrates via a chaingrowth mechanism, thereby providing a path for pretreating water by flocculating out contaminants with concurrent generation of hydrogen.

Recent advances in the design and use of Pickering emulsions for wastewater treatment applications

“…Alternatively, a new reaction system for the simultaneous removal of aromatic contaminants from wastewater was demonstrated by carrying out a photo-induced oxidative polymerization of phenolic substrates via a chain growth mechanism, thereby providing a path for pretreating water by flocculating out contaminants with a concurrent generation of hydrogen. 125 The propagating polymer chain would exhibit a decreasing water-solubility pattern with each added monomer up to a point, where a poly-phenolic Pickering emulsion from the contaminants originally found in wastewater could be formed. Additionally, the reaction results in generation of hydrogen gas, which can be utilized as a useful byproduct.…”

Flexible Sponge Ball-like Temperature-Responsive Molecularly Imprinted Polymer with Self-Driven “Transformation Recovery” and Mechanism Exploration

“…With the rapid development of industrial technology, p-NP (p-nitrophenol), as one of the most toxic nitrophenols, has been frequently detected in the industrial wastewater in the field of medicine, dyestuffs, chemosynthesis, and pesticides. , The characteristics of difficult natural degradation stability facilitated p-NP gathering in the human body, which could easily cause nausea and inhibit the central nervous system of the human body to make irreversible damage . Due to the strong stability and water solubility, diverse techniques have been employed to eliminate the phenolic compound in industrial wastewater, such as catalytic degradation, , catalytic reduction, discharge plasma, liquid–liquid extraction, etc.…”

Generation and Use of Lignin-g-AMPS in Extended DLVO Theory for Evaluating the Flocculation of Colloidal Particles

“…Owing to its cost-effectiveness and ease of operation, flocculation is the most commonly used technique to achieve an efficient solid–liquid separation in many industrial processes, such as coal mining and mineral processes, wastewater treatment, − pulp and paper processes, and biotechnology operations . In these processes, flocculants are essential elements to destabilize suspended colloids.…”

“…Charge neutralization, polymer bridging, and electrostatic patch have been described as the primary mechanisms of flocculation processes. ,, It is widely accepted that polymeric flocculants develop flocs with different properties when adsorbed onto particles . Hydrodynamic and short-range interactions are considered to be the major factors for the collision of flocculants and particles .…”

“…The optimal process conditions were 2.5 mol/mol AMPS/lignin, 0.6 g/g solid/water ratio, 2.0 initiator/lignin weight ratio, 80 °C, 120 min, and pH 1.5, which yielded KL-g-AMPS with the anionic charge density of 4.28 mequiv/g and the grafting ratio of 285%. The chemical structure and compositions of the polymers were confirmed by 1 H NMR and elemental analysis. The flocculation performance of the polymer was evaluated in an aluminum oxide suspension, and its performance was compared with that of a homopolymer of AMPS produced under the same conditions.…”