Hybrid functionalized phosphonate silica: insight into chromium removal chemistry from aqueous solutions

Abstract

Abstract. Insight into Cr(III) ions removal chemistry from aqueous solutions was gained by using hybrid phosphonate-functionalized silica adsorbents synthesized through a modified route of sol-gel processing (SPMF). Evaluation of the degree of metal removal was obtained from kinetics and batch experiments. Elemental analysis, FTIR, NMR and XPS techniques were used to study the nature of surface complex formed on adsorbent. Adsorption equilibrium results showed a maximum Cr(III) removal of 78.639 mg g-1Cr(III) at pH 3.6 on adsorbent SPMF04; kinetics measurements indicated that equilibrium was reached in 80 min contact time. The achievement of 2.923 mmol P/g as phosphonate groups was obtained. A Langmuir-type mechanism explained the adsorption equilibrium results whereas kinetic measurements were explained through a pseudo-second order mechanism. FTIR measurements indicated a strong influence of Cr(III) adsorbed on surficial functional groups. 29Si CP MAS NMR results indicated that Cr(III) interacted not only with phosphonate surface groups but also with a large of amount of geminal OH surface groups. XPS studies suggested that Cr(III) was removed through the formation of the surface complex R as monovalent chromium acetate and/or divalent. The adsorbent SPMF04 can be potentially employed in industrial applications. 
 Resumen. Información sobre la química de remoción de Cr(III) de soluciones acuosas fue obtenida usando adsorbentes de sílice hibrida funcionalizada con fosfonato sintetizados a través de una ruta modificada del proceso sol-gel (SPMF). La evaluación del grado de remoción de metal fue obtenida a partir de experimentos de cinética y por lotes. Técnicas de análisis elemental, FTIR, NMR y XPS fueron usadas para estudiar la naturaleza del complejo de superficie formado sobre el adsorbente. Los resultados del equilibrio de adsorción mostraron una remoción máxima de Cr(III) de 78.639 mg g-1 Cr(III) a pH 3.6 sobre el adsorbente SPMF04; las mediciones cinéticas indicaron que el equilibrio fue alcanzado en 80 min de tiempo de contacto. El logro de 2.923 mmol P/g como grupos fosfonato fue obtenido. Un mecanismo tipo Langmuir explicó los resultados del equilibrio de adsorción mientras que las mediciones cinéticas fueron explicadas a través de un mecanismo de pseudo-segundo orden. Los resultados de 29Si CP MAS NMR indicaron que Cr (III) interactuó no solamente con grupos fosfonato de superficie sino también con una gran cantidad de grupos OH de superficie geminales. Los estudios de XPS sugirieron que Cr(III) fue removido a través de la formación del complejo de superficie R como acetato de cromo monovalente y/o divalente. El adsorbente SPMF04 puede ser potencialmente empleado en aplicaciones industriales.

Boosted Hydrogen‐Evolution Kinetics Over Particulate Lanthanum and Rhodium‐Doped Strontium Titanate Photocatalysts Modified with Phosphonate Groups

“…Therefore, improved HER rate by the phosphonate‐based silane coupling treatment should be mainly attributed to the existence of the phosphonate groups, separately from some interactions with the Ru species. Here, it should be noted that the commercially available silane coupling reagents used in the present study have been already reported to be anchored on the oxide surface through the silanol groups [32–37] . The Fourier‐transform infrared (FTIR) observations confirmed that the adsorbent modified with the present silane coupling reagents certainly showed consistent IR absorption to the reported cases (Figure S4), [32–37] indicating that the present silane coupling reagents should be anchored on the photocatalysts surface through the silanol group as is similar to the reported cases of the oxide materials functionalized by these silane coupling reagents [32–37] .…”

“…Here, it should be noted that the commercially available silane coupling reagents used in the present study have been already reported to be anchored on the oxide surface through the silanol groups [32–37] . The Fourier‐transform infrared (FTIR) observations confirmed that the adsorbent modified with the present silane coupling reagents certainly showed consistent IR absorption to the reported cases (Figure S4), [32–37] indicating that the present silane coupling reagents should be anchored on the photocatalysts surface through the silanol group as is similar to the reported cases of the oxide materials functionalized by these silane coupling reagents [32–37] . Nevertheless, since the loading conditions of the silane coupling reagents (e.g., organization and/or coverage) may affect the overall catalytic performances, further evidence regarding surface anchoring state will be required to establish more detailed information about the effects of the functional groups other than phosphonate (such as amine, sulfonate, and propyl moieties) in future.…”

Synthesis of a New Phosphonate-Based Sorbent and Characterization of Its Interactions with Lanthanum (III) and Terbium (III)

“…XPS spectroscopy can be used not only for the characterization of the sorbent but also for the identification of binding mechanisms [ 66 , 67 ]. The sorption mechanisms can be also approached by the variations in the XPS spectra of the sorbents exposed to La (III) and Tb(III) solutions for selected signals ( Figure 9 , survey spectra, Figure 10 and Figure 11 HRES XPS spectra, and Table S9 ).…”

For Whom a Puddle Is the Sea? Adsorption of Organic Guests on Hydrated MCM-41 Silica

“…The observed temperature and hydration effects on adsorption are of practical importance. Adsorption of phosphate groups, , pharmaceutical substances, , and DNA − on silica, removal of impurities from polluted water, − and environmental safety of sediments , are humidity-sensitive. Another potentially important type of guests are molecules, which exhibit self-assembling ability in aqueous solutions. − Such molecules have remained outside the scope of this work.…”