Leaching of nanoparticles from nano-enabled products for the protection of cultural heritage surfaces: a review

Brunelli, Andrea; Calgaro, Loris; Semenzin, Elena; Cazzagon, Virginia; Giubilato, Elisa; Marcomini, Antonio; Badetti, Elena

doi:10.1186/s12302-021-00493-z

Environmental Sciences Europe

Table 2 Studies with non-standardized procedures to estimate NPs leaching from nano-enabled products

From: Leaching of nanoparticles from nano-enabled products for the protection of cultural heritage surfaces: a review

Nano-enabled product	Substrate	Tested media	Experimental procedure	Time of leaching evaluation	Elements/NPs detection and analytical techniques	Species detected in the leachate	Literature source
Immersion test procedures
Ag nanocomposite films	Stainless steel	NaCl 0.15 M solution	Immersion of 10 × 10 mm (0.9 mm thickness)	60 days	¹⁰⁸Ag⁻ detection by XPS and ToF-SIMS	Ionic form: Ag	Zanna et al. [83]
TiO₂ NPs coatings	Glass substrate	DW, DW with humic acids and NaCl	Immersion of 30 × 25 mm tiles	1–4 weeks	Total [Ti] by ICP-OES	Ionic form: Ti	Olabarrieta et al. [50]
TiO₂ NPs coatings	Glass substrate	DW, DW with humic acids and NaCl	Immersion of 30 × 25 mm tiles	1–4 weeks	TiO₂ NPs by SEM-EDX	Free NPs: TiO₂	Olabarrieta et al. [50]
Ag NPs	Glass	DW, phosphate buffer (pH 7.4, 1.25 mM KH₂PO₄, 2.5 mM K₂HPO₄, 4.7 mM Na₂HPO₄, supplemented with 0.4% glucose)	Immersion of 1 × 1 cm² glass substrates	60 min	Total [Ag] by ICP-AES	Ionic form: no significant amount of Ag	Agnihotri [58]
Ag NPs	Glass		Immersion of 1 × 1 cm² glass substrates	60 min	Ag NPs by FEG-TEM and FEG-SEM	Ionic form: no significant amount of Ag	Agnihotri [58]
TiO₂ NPs-based paints	Fibre cement panels	DW, tap water, rain water	Immersion of 10 × 10 cm	113 cycles of 6 h each (3 h of UV light, 0.5 h of irrigation and 2.5 h of drying)	Total [Ti] by ICP-OES	Ionic form: very low amount of Ti	Al-Kattan et al. [51]
TiO₂ NPs-based paints	Fibre cement panels	DW, tap water, rain water	Immersion of 10 × 10 cm		TiO₂ NPs by TEM–EDX	Ionic form: very low amount of Ti	Al-Kattan et al. [51]
Ag nanocomposite	Ag–chitosan film	DW	Immersion of film	24 h	Total [Ag] by UV–Vis	Ionic form: Ag, especially with low MW chitosan	Regiel et al. [82]
Ag NPs-based antimicrobial material	Hyperbranched epoxy	Phosphate buffer saline, synthetic seawater	Immersion of 1 × 1 cm	7 days	Total [Ag] by UV–Vis	Ionic form: Ag	Barua et al. [84]
Ag NPs-based coatings	Wood panels	Rain water	Immersion of facade elements with an area of 0.75 × 1.44 m²	1 year—outdoor	Total [Ag] by ICP-MS	Ionic form: Ag	Künniger et al. [48]
Ag NPs-based coatings	Wood panels	Rain water	Immersion of facade elements with an area of 0.75 × 1.44 m²	1 year—outdoor	Ag NPs detection by TEM	Ionic form: Ag	Künniger et al. [48]
Ag NPs-based coatings	Polystyrene, glass, metal binder clips	Seawater	Immersion of 20 cm diameter petri dishes	120 h	Total [Ag] by AAS	Ionic form: Ag	Ren et al. [85]
Chitosan–zinc oxide nanocomposite coatings	Glass substrate	DW	Immersion of 25 × 75 mm coated slides	0–4 weeks	Total [Zn] by ICP-OES	Ionic form: Zn	Al-Naamani et al. [86]
Diketopyrrolopyrrole, Fe₂O₃ NPs-based pigments	Polymer matrix	Food simulants: DW, DW with 10% EtOH, DW with 3% acetic acid; environmental media: DW, moderately hard water (pH 7.6) and DW+SRNOM, pH 8)	Immersion of plates, granules and fragments	Food simulants: 10 days	Fe₂O₃ NPs-based fragments detection by TEM, UV–Vis, AUC, ICP-MS, spICP-MS	Ionic form: Fe	Neubauer et al. [52]
Diketopyrrolopyrrole, Fe₂O₃ NPs-based pigments	Polymer matrix		Immersion of plates, granules and fragments	Environmental media: 3 months		Free NPs: Fe particles	Neubauer et al. [52]
MWCNT	Epoxy and polyamide polymers	Rain water	Immersion of MWCNT-based polymers	Toxicity characteristic leaching procedure extraction fluid #1: 24 h + 1 h	TEM to identify the form of release	Ionic form: Al, Co, Fe	Wohlleben et al. [54]
					ICP-MS to quantify Al and Co, tracers for MWCNTs	Free NPs: only MWCNTs from epoxy-MWCNT
					UV–Vis/turbidity to semi-quantitatively rank the release quantity AUC or AF4 to quantify the free ENMs category by size-selectivity	Embedded in matrix: epoxy-MWCNT and polyamide-MWCNT
TiO₂ NPs coatings	Silicon substrates	DW, Acid rain solution (EPA method 1320), boiling water for industrial test conditions	Immersion of 20 × 20 mm silicon substrates	7 days	Total [Ti] by ICP-OES	Ionic form: Ti	Cedillo-González et al. [87]
TiO₂ NPs coatings	Silicon substrates		Immersion of 20 × 20 mm silicon substrates	1 h for boiling water	Total [Ti] by ICP-OES	Ionic form: Ti	Cedillo-González et al. [87]
CeO₂ NPs	Micronized copper-azole pressure treated lumber, composite decking material	Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Total [Ce] by ICP-OES	Ionic form: Ce	Clar et al. [88]
					Speciation analysis by XAFS	Embedded in the matrix: aggregates with also Ce signal
					CeO₂ aggregates by BSE-FESEM–EDX	Embedded in the matrix: aggregates with also Ce signal
Cu NPs	Lumber treated with Cu	DW, 1, 10 and 30 ‰ seawater	Immersion of 2 × 2 × 2 cm lumber blocks	8 h, 1, 2, 7, 14, 28 and 133 days	Total [Cu] by ICP-AES	Ionic form: Cu	Parks et al. [89]
ZnO NPs	Micronized copper-azole pressure treated lumber, composite decking material	Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Total [Zn] by ICP-OES	Ionic form: Zn	Clar et al. [90]
					Speciation analysis by XAFS	Embedded in the matrix: aggregates with also Zn signal
					ZnO aggregates by BSE-FESEM–EDX	Embedded in the matrix: aggregates with also Zn signal
ZnO NPs	Micronized copper azole-treated lumber, aqueous copper azole-treated lumber	Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Total [Zn] and [Cu] by ICP-OES	Ionic form: Zn	Clar et al. [91]
ZnO NPs		Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Speciation analysis by XAFS	Ionic form: Zn	Clar et al. [91]
Diketopyrrolopyrrol, Cu-phthalocyanine, Fe₂O₃ NPs pigments	Acrylic and melamine coatings	Nanopure water with sodium dodecyl sulfate	Immersion of 7 × 8 cm and 10 x 9 cm plates	1 and 12 h	Nano-based fragments by TEM–EDX, UV–Vis and AUC	Embedded in the matrix: fragments, potentially with embedded pigments	Ruggiero et al. [53]
Polystyrene–TiO₂ NPs coatings	Aluminium alloy	3.5 wt % NaCl aqueous solution	Immersion of Al alloy samples	6 h, 1 and 3 days	Corrosion by XRD, EDX and EIS	Not determined	Zhang and Zhang [92]
TiO₂ NPs	Oak slats	Indoor: DW Outdoor: Rain and snow melt waters	Immersion of 0.64 cm thick × 6.4 cm wide oak slats	2, 4, 7 and 10 weeks in winter—2 weeks in summer—outdoor	TiO₂ NPs by spICP-MS	Ionic form: Ti	Azimzada et al. [49]
TiO₂ NPs	Oak slats	Indoor: DW Outdoor: Rain and snow melt waters	Immersion of 0.64 cm thick × 6.4 cm wide oak slats	2, 4, 7 and 10 weeks in winter—2 weeks in summer—outdoor	TiO₂ NPs by spICP-MS	Free NPs: TiO₂	Azimzada et al. [49]
PET-Ag NPs fibres	Textiles	DW	Immersion of 38 mm length PET fibres	15 min, 30 min, 2 h, 8 h, 12 h and 24 h	Total [Ag] by ICP-MS	Ionic form: Ag	Gadkari et al. [93]
Ag NPs	Cellulose membranes	Bacterial suspension	Immersion of cellulose membrane filters	24, 48, 72, 96 h	Indirect measurements by SEM, TGA and EDX	Not determined	Hanif et al. [94]
ZnO NPs	Micronized copper azole pressure treated lumber	Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Total [Zn] and [Cu] by ICP-OES	Ionic form: Zn	Thornton et al. [95]
ZnO NPs	Micronized copper azole pressure treated lumber	Synthetic precipitation liquid procedure solution	Immersion of 4 × 4 cm coupons	72 h	Speciation analysis by XAFS	Ionic form: Zn	Thornton et al. [95]
Water spray or/and outdoor runoff methods
Ag NPs-based paint	Façade panels	Rain water	Runoff from outdoor façades	1 year under natural outdoor weather conditions	Total [Ag] and [Ti] by ICP-MS	Ionic form: Ag, Ti	Kaegi et al. [8]
					Ag NPs by TEM–EDX	Free NPs: Ag
					Ag NPs by TEM–EDX	Embedded in the matrix: Ag NPs attached on the organic binder
SiO₂ NPs	Epoxy-based material	DW	Water spray on amine-cured epoxy containing nanocoating (10 cm diameter)	–	Total [Si] by ICP-OES	Ionic form: Si	Sung et al. [81]
TiO₂ NPs	Brick, concrete panels	DW	Water spray on masonry brick (11 cm × 5 cm × 5 cm)	At selected time points of the weathering process: 2, 4, 6 and 7 months	Total [Ti] by ICP-MS	Ionic form: Ti	Shandilya et al. [55]
TiO₂ NPs	Brick, concrete panels	DW	Water spray on masonry brick (11 cm × 5 cm × 5 cm)		TiO₂ NPs by TEM–EDX	Embedded in the matrix: particle agglomerates	Shandilya et al. [55]
TiO₂ NPs	Photocatalytic pavements	Rain runoff high-pressure water cleaning	Runoff on 4 × 4 m slabs	800 days	Total [Ti] by ICP-MS	Ionic form: Ti	Jimenez-Relinque et al. [56]
TiO₂ NPs	Photocatalytic pavements	Rain runoff high-pressure water cleaning	Runoff on 4 × 4 m slabs	800 days	TiO₂ NPs by FE-SEM and EDX	Embedded in the matrix: particles containing Ti	Jimenez-Relinque et al. [56]
ZnO-graphene oxide nanocomposites	ZnO, rGO and ZnO–rGO functionalized surfaces	DW	Aerosol spray on 1 × 1 cm glass substrate	20 h	[Zn²⁺] in μg/cm² by TXRF	Ionic form: Zn	Valenzuela et al. [96]
Leaching from milled paint/aged particles in contact with a liquid
TiO₂ NPs-based paints	Paints	DW, 10 mM NaCl, 3 mM CaCl₂	Extractability of Ti from aged milled paint dispersed in waters	3 days shaken + 24 h rest to obtain supernatant	Total [Ti] by ICP-MS	Ionic form: Ti	Al-Kattan et al. [57]
					TiO₂ NPs by STEM–EDX	Free NPs: TiO₂
					TiO₂ NPs by STEM–EDX	Embedded in the matrix: TiO₂ NPs
SiO₂ NPs-based paints	Fibre cement panels	Tap water, DW	Water spray on treated panels (195 × 75 cm)	46 L for 89 cycles of 6 h each	Total [Si] by ICP-MS	Ionic form: Si	Al-Kattan et al. [5]
			Extractability of Si from aged milled paint	24 h stirring + 24 h rest to obtain supernatant	Elemental composition by XRF	Free NPs: SiO₂
			Extractability of Si from aged milled paint	24 h stirring + 24 h rest to obtain supernatant	SiO₂ NPs by STEM–EDX	Embedded in the matrix: SiO₂ NPs
SiO₂ NPs	Silicate coating	DW, tap water, soap solution, 0.5 M nitric acid, artificial sea and rainwaters	Leaching from particles	Rotating mixer for 1 h (tap water, soap solution, and 0.5 M nitric acid), 72 h (artificial sea and rain water) or 30 days (DW)	Gamma counter, SEM and DLS	Not determined	Jolin et al. [97]
Leaching in contact with water-based liquid
TiO₂ NPs-based paints	PVC and glass substrates	Wet (2.5 g/l of dodecylbenzenesulfonate of sodium) and dry conditions	Solution spread onto the coating	37 abrasion cycles/min	NPs by laser granulometer and SEM	Embedded in the matrix: TiO₂ NPs	Golanski et al. [98]
TiO₂ NPs and hydroxyapatite	Marble	Simulated rain	Drip DW over 30 × 30 × 20 mm samples	Simulated 6 years rain	Total [Ti] by ICP-OES	Ionic form: Ti	Sassoni et al. [59]
TiO₂ NPs and hydroxyapatite	Marble	Simulated rain	Drip DW over 30 × 30 × 20 mm samples	Simulated 6 years rain	TiO₂ NPs by EDX	Ionic form: Ti	Sassoni et al. [59]
CuO:Ag NPs	Activated carbon	DW	Flushed water	10 l of water contaminated with E. coli; 600 l of uncontaminated water; 10 l of contaminated water	Total [Ag] and [Cu] by AAS	Ionic form: Ag and Cu	Arakawa et al. [99]
Cu NPs, Cu₂O NPs and CuO NPs	LLDPE polymer	Saline solution and bacterial suspensions	Thickness between 0.2 and 0.5 mm of PE with NPs in contact with water	Mixing by magnetic stirrer over 1 month	Total [Cu] by ICP-AES	Ionic form: Cu	Gurianov et al. [100]
Ag NPs	Textiles	DW and detergent solution	5 × 5 cm of cotton print cloth in a PP bottle with 15 ml of DW or detergent solution	Samples in a plastic bottle with 15 ml of DW or detergent solution with glass balls to simulate frictions of home laundering	Total [Ag] by ICP-MS	Ionic form: Ag	Nam et al. [60]
Ag NPs	Textiles	DW and detergent solution			Ag NPs by SERS	Embedded in the matrix: Ag NPs complexed with detergent components	Nam et al. [60]

Immersion test, water spray and/or runoff methods, leaching from milled paint/aged particles in contact with a liquid and leachate from nano-enabled products in contact with a water-based liquid were the four non-standardized procedures categories identified
AAS Atomic absorption spectroscopy; AUC Analytical ultracentrifugation; DW Deionized water; EDX Energy dispersive X-ray spectroscopy; EIS Electrochemical impedance spectroscopy; FEG-SEM Field emission scanning electron microscopy; FEG-TEM Field emission gun-transmission electron microscopy; FTIR Fourier-transform infrared spectroscopy; ICP-OES Inductively coupled plasma-optical emission spectroscopy; ICP-AES Inductively coupled plasma atomic emission spectroscopy; LLDPE Linear low-density polyethylene; spICP-MS Single particle inductively coupled plasma-mass spectrometry; SERS Surface enhanced Raman spectroscopy; TGA Thermogravimetric analysis; ToF–SIMS Time of flight-secondary ion mass spectrometry; TXRF Total reflection X-ray fluorescence UV–Vis Ultra violet–visible spectroscopy; XRD X-ray diffraction; XPS X-ray photoelectron spectroscopy; XAFS X-ray absorbance fine structure

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