Dissolution and Microstructural Transformation of ZnO Nanoparticles under the Influence of Phosphate

Abstract

ABSTRACT:The toxicity and fate of nanoparticles (NPs) have been reported to be highly dependent on the chemistry of the medium, and the effects of phosphate have tended to be ignored despite the wide existence of phosphate contamination in aqueous environments. In the present study the influence of phosphate on the dissolution and microstructural transformation of ZnO NPs was investigated. Phosphate at a low concentration rapidly and substantially reduced the release of Zn 2+ into aqueous solution. Synchrotron X-ray absorption spectroscopy and X-ray diffraction analysis reveal that interaction between ZnO NPs and phosphate induced the transformation of ZnO into zinc phosphate. Transmission electronic microscopy observation shows that the morphology of the particles changed from structurally uniform nanosized spherical to anomalous and porous material containing mixed amorphous and crystalline phases of ZnO and zinc phosphate in the presence of phosphate. To our knowledge, this is the first study in which the detailed process of phosphate-induced speciation and microstructural transformation of ZnO NPs has been analyzed. In view of the wide existence of phosphate contamination in water and its strong metal-complexation capability, phosphate-induced transformations may play an important role in the behaviors, fate, and toxicity of many other metal-based nanomaterials in the environment.

Chemical transformation of zinc oxide nanoparticles as a result of interaction with hydroxyapatite

“…However, the diagnostic peaks of ZnO (Fig. 2, dashed [14]. Moreover, the molar ratio of the sequestered contents of PO 4 3− and Ca 2+ Fig.…”

“…The reduction in the concentrations of PO 4 3− and Ca 2+ suggested the coprecipitation of Zn 2+ released from ZnO NPs with PO 4 3− and Ca 2+ at pH 5. We speculated that sequestration of the released Zn 2+ from solution would induce further dissolution of ZnO NPs and accelerate chemical transformation of ZnO NPs, similar to the role of PO 4 3− in sequestering Zn 2+ released from ZnO NPs [14]. However, HAP only dissolved to a very small extent with PO 4 3− concentration detected at 0.67 and 0.75 mg L −1 in the ZnO NPs/HAP suspensions at pH 7 and 9, respectively, so that coprecipitation of Zn 2+ with PO 4 3− and Ca 2+ might be insignificant.…”

“…ZnO nanoparticles were purchased from Nachen Sci & Tech Co. (Beijing, China) with a purity of 99.9%, the same as described previously [14]. The HAP used was purchased from Sinopharm Chemcial Reagent Co. Ltd (Shanghai, China).…”

“…Standard XAFS data reduction procedures were undertaken using the program package IFEFFIT [23], and WinXAS v 3.1 [24] was used for data fitting. Detailed processes were described previously [14,25]. Simply, background removal, normalization, cubic spline conversion and forward Fourier transform of the k 3 (k) spectra from 2.4 to 12.5Å −1 using Bessel window were performed to obtain the radial distribution function (RDF) in R-space.…”

“…For example, studies have demonstrated the transformation of ZnO NPs to ZnS in the presence of sodium sulfide (Na 2 S) or hydrogen sulfide (H 2 S) [12,13]. Our previous research [14] has confirmed that phosphate ions can induce the transformation of ZnO NPs to tetrahydrate Zn 3 (PO 4 ) 2 in aqueous solutions at room temperature and under neutral pH conditions. Very recently, Rathnayake et al [15] also observed that phosphate ions induced transformation of ZnO NPs to Zn 3 (PO 4 ) 2 and further indicated that such transformation was pH dependent and crystalline hopeite preferred to form at pH 6 rather than at pH 8.…”