Fe₃O₄Nanoparticles Dispersed on Douglas Fir Biochar for Phosphate Sorption

Abstract

Surface area, particle aggregation, pressure drop in columns, nanotoxicity, and commercialization difficulties limit the use of nanoparticle adsorbents. Magnetic primary nano-Fe3O4 particles (∼16.7 nm diameter) were dispersed on high-surface-area (695 m2/g) Douglas fir biochar (MBC). A cheap, commercial fast pyrolysis biochar, a syngas byproduct, was modified by chemical coprecipitation of Fe3O4 from Fe3+/Fe2+ aqueous NaOH, served as a matrix, aiding magnetite nanoparticle dispersion and reducing the extent of particle aggregation. This MBC removed ∼90.0 mg/g of phosphate from water, approximately 20 times the capacity reported for neat (∼39 nm) magnetite particles (∼5.1 mg/g). MBC was robust in fixed-bed column sorption with 82.5 mg/g (at pH 3) capacity, showing no significant equilibrium or kinetic limitations in flow versus batch sorption. The biochar support serves as an added adsorption phase for heavy metals and organic contaminants, adsorbing poorly on magnetite. MBC enables magnetic separation of exhausted adsorbent from a batch process, an alternative to filtration. The neat and phosphate-laden hybrid sorbents were was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, point of zero charge, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), elemental analysis, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface-area and pore-volume measurements. The chemisorption mechanism versus pH, evaluated by XPS and existing literature, characterized the dominant phosphate complexes adsorbed on magnetite. The pH effect on phosphate sorption and the P 2p XPS binding energy shifts at pH from 1 to 13 are reported. A solution pH of 1–3 facilitates the formation of bidentate monoprotonated phosphate complexes [(Fe–O)2-PO2H]− at Fe–OH surface functions. H2PO4 2– predominates in solution at pH ∼4–6.5, which favors the formation of [Fe–O–PO3H]− at these pH values. At strongly basic pH (10–13) values, PO4 3– predominates and forms deprotonated chemisorbed monodentate [Fe–O–PO3]2– and bidentate [(Fe–O)2PO2]2–. Multilayer phosphate sorption and precipitation of iron phosphates were considered.

Simplified Batch and Fixed-Bed Design System for Efficient and Sustainable Fluoride Removal from Water Using Slow Pyrolyzed Okra Stem and Black Gram Straw Biochars

“…The fixed-bed parameters including total time ( t x ), mass flow rate ( F m ), time required for PAZ movement ( t δ ), depth (δ), time needed for initial PAZ formation ( t f ), amount of fluoride adsorb ( M s ), column fractional capacity ( f ), percent saturation, empty-bed-contact-time (time required for influent to be in contact with biochar bed), and biochar usage rate were calculated using eqs 4–10. 46,80−84 …”

The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

“…Results of an ATR-FTIR analysis showed that calcium carbonate was a main adsorption site for phosphorus of Mallee biochar, which represented a 16% increase in phosphorus adsorption and more than 50% of which were accessible to plant uptake in Mallee biochar (5% w/w) conditioned soils [108]. Surface activation by chemicals, such as metal salts, alkali, and nano-particles, significantly enhanced the phosphorus adsorption capacity of biochar [105,106,[110][111][112]. Phosphate adsorption capacity increased from 2.1% of untreated to 70.3% of magnesium treated Oak biochar [106].…”

“…Results on phosphorus removal from secondary wastewater effluents by biochar loaded with colloidal and nano-sized aluminum oxyhydroxide crystalline flakes showed that, in less than 8 h, 8.3 g of phosphorus was adsorbed per kg of engineered biochar in a fixed-bed column [112]. Loading biochar with magnetic nano-particles increased phosphate adsorption capacity by 20-fold compared to that of nano-magnetite [110]. Furthermore, the pyrolysis of poultry litter biomass with phosphate, phosphoric acid, and magnesium oxide strongly decreased dissolved phosphorus concentrations due to the strong adsorption and slow-release of phosphate in soils, which facilitated the phosphorus utilization rate [113].…”

Composite Nanofibers: Recent Progress in Adsorptive Removal and Photocatalytic Degradation of Dyes

“…Similarly, the pH PZC of MgO is 12.4, and the anionic dye adsorption is driven by electrostatic forces. The pH PZC of TiO 2 is around neutral values (6-6.8), which is not so much different from those of iron oxides; the PZC values measured for FeO, Fe 3 O 4 , and Fe 2 O 3 were around 6.1-6.5 [28,29]. The pH PZC of TiO 2 and iron oxides is in the neutral range, making them efficient adsorbents for both cationic and anionic dyes in a wide range of pH mediums.…”