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Building and Environment 93 (2015) 119e127

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Building and Environment

journal homepage: www.elsevier .com/locate/bui ldenv

Comparison of resistance improvement to fungal growth on green andconventional building materials by nano-metal impregnation

Hsiao-Lin Huang a, Chi-Chi Lin b, *, Kunnan Hsu b

a Department of Occupational Safety and Health, Chia Nan University of Pharmacy & Science, No.60, Sec. 1, Erren Rd., Rende Dist., Tainan City 71710, Taiwanb Department of Civil and Environmental Engineering, National University of Kaohsiung, No. 700, Kaohsiung University Rd., Kaohsiung, Taiwan

a r t i c l e i n f o

Article history:Received 3 May 2015Received in revised form15 June 2015Accepted 17 June 2015Available online 20 June 2015

Keywords:Antifungal abilityAspergillusPenicilliumNano-metalBuilding material

* Corresponding author.E-mail address: chichilin@nuk.edu.tw (C.-C. Lin).

http://dx.doi.org/10.1016/j.buildenv.2015.06.0160360-1323/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

This study is aimed for comparing the biological resistance of green and conventional building materials(BMs) before and after nano-metal treatment, as well as exploring best nano-metals to improve fungalgrowth resistance of BMs. The selected BMs include wooden flooring (WF), green wooden flooring(GWF), gypsum board (GB), green gypsum board (GGB), calcium silicate board (CSB), green calciumsilicate board (GCSB), mineral fiber ceiling (MFC) and green mineral fiber ceiling (GMFC). The Aspergillusbrasiliensis or Penicillium funiculosum was inoculated on each sample and their growth was visuallyevaluated according to ASTM G21-09.

The fungal growth without nano-metals on test materials did not show that green materials weremore prone to fungal growth. After nano-metal treatment, the observed order of fungal growth resis-tance of nano-metals at their highest selected concentrations on test materials was nano-zinc ¼ nano-copper > nano-silver for WF and GWF, nano-zinc > nano-silver ¼ nano-copper for GB, nano-zinc > nano-silver > nano-copper for GGB, CSB and GCSB, nano-silver > nano-copper ¼ nano-zinc for MFC, and nano-silver > nano-copper > nano-zinc for GMFC. Nano-zinc seems to be the most favorable nano-metal forwood and wood composite materials. Green materials were less resistant to fungi attack relative to theirconventional counterparts treated by nano-metals, particularly GWF and WF. All test nano-metals failedto provide complete protection against fungal growth on the eight test BMs at the selected concentra-tions. However, the higher the nano-metal concentration was, the longer the lag period until growthbegan and fewer fungi grew on the materials.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Due to global climate change, extremely heavy rains and floodsbecome more and more frequent worldwide, such as HurricanesKatrina and Rita in the Gulf Coast of the Unitest States, and TyphoonMorakot in southern Taiwan. Serious water damages and dampnessin buildings have caused heavy fungal growth on buildingmaterials[1e6]. Fungal propagation can adversely affect the health ofbuilding occupants, including allergic symptom asthma, bronchipulmonary aspergillosis and respiratory infection [7e17], and causediscoloration and deterioration of building materials [18e21].

Many studies have shown that fungi can easily grow on a varietyof building materials, including conventional and green building

materials [15,22,23]. Factors that affect fungal growth includemoisture, material type, spore levels and fungal species[15,19,22,24e27]. Moisture has an impact on microbial growth byincreasing both the concentration and diversity of microorganismson water damaged surfaces [28e30]. Besides moisture, the mainreason is that building materials such as ceiling tiles and woodmaterials which are organic compounds that can provide sufficientnutrients to support fungal growthwhether the buildingmaterial islabeled as green or conventional [23,31,32]. Correlations betweenbuilding material types and fungal species present have beenexplored in some studies. Species of Penicillium are commonlyfound in various building materials [33e36]. Aspergillus species arefrequently recovered on ceramic-type materials (concrete, mortar)and glues and paints [34,36]. Conventional antifungal additives toprevent fungal growth are often added in building materials, suchas sodium polyborate, dichlofluanid, and so on [32,37e40]. How-ever, the popularity of antifungal additives for indoor uses is limiteddue to its short-term effectiveness and potential health concerns

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127120

[37,39]. Nanotechnology offers great opportunities for new anti-fungal additives with enhanced properties compared to conven-tional ones. Specific characteristics of nano-metals include highsurface to volume ratio, homogeneous particles size distributionpossibility of facile surface medication, good stability and the easeof preparation. These unique properties offer nano-metals greatapplication in many fields. For example, nano-metals (e.g. silver,copper and zinc) has been wildly applied to improve the physicaland mechanical properties of various materials, such as paper,archaeological stones, coatings, woods and wood composites[41e49]. It is generally believed that nanoparticles of these metalsinteract with the bacterial membrane elements, resulting in thestructural changes leading to the cell death. Also, these nano-particles are small enough to damage cell membranes and furtherdisrupt the enzyme function [50,51]. In addition, photocatalyticoxidation by TiO2 are often used to deactivate biological pollutants.On the other hand, the photocatalytic reaction is not sufficient fortotal disinfection against mold fungi since usually there is no visiblefungi growth specimens during the photo-process but fungi canregrow once the light source (i.e., UVA at 365 nm) gets removed[52]. However, due to the particle sizes of nano-metals, a negligibletotal mass of nanoparticles released intentionally or incidentallymay contain high numbers of them that can nonetheless affecthuman health [53e59], mainly through inhalation exposure [60].Nevertheless, the correct use of nanomaterials not only offer strongantibacterial activity and low toxicity towards mammalian cells,but also provide a great potential in adsorption and degradation ofenvironmental pollutants as they exhibit catalytic activity [61].

Although many studies about fungal growth or impact factorsfor fungal growth on building materials have been performed,such as quartz/putty [62], wood [63], cement based board andgypsum plaster board [64], ceiling tiles and wallboard cabinetry[23], studies on the biological resistance comparison of nano-metals on both conventional and green building materials arerather few. In this study, the biological resistance of green andconventional building materials (BMs) was compared before andafter impregnation of single kind of nano-metal (i.e., Ag, Cu, andZn) on Aspergillus brasiliensis (BCRC 31512) and Penicillium funi-culosum (BCRC 30438) were tested which are ubiquitous in indoorair environment and can cause negative human health effects. Theselected building materials include wooden flooring (WF), greenwooden flooring (GWF), gypsum board (GB), green gypsum board(GGB), calcium silicate board (CSB), green calcium silicate board(GCSB), mineral fiber ceiling (MFC) and green mineral fiber ceiling(GMFC). This study will provide useful information for comparingthe green and conventional materials in terms of fungal growthresistance before and after nano-metal treatment. It also helpschoose best nano-metals to improve fungal resistance of buildingsmaterials.

2. Experimental methodology

2.1. Building materials

Four different conventional materials and green counterpart foreach conventional material were tested: wooden flooring (WF),green wooden flooring (GWF), calcium silicate board (CSB), greencalcium silicate board (GCSB), gypsum board (GB), green gypsumboard (GGB), mineral fiber ceiling (MFC), and green mineral fiberceiling (GMFC).“Green” specifically refers to low emission healthygreen building materials which are rated by Taiwan Architectureand Building Center. All materials were unused and were shippeddirectly from three major manufacturers in Taiwan. Materials werewrapped in two layers of aluminum foil and one layer of plasticsheeting before experiments carried out. Table 1 provides

information on the basic composition and density of the testmaterials.

All selected materials are commonly used for ceiling, cabinetry,and flooring. Each specimen of BM was cut into identical sizes(5 cm � 5 cm) for testing. The thickness is 0.9 cm, 0.6 cm, 0.9 cm,0.9 cm, 0.7 cm, 1.1 cm, 1.2 cm and 1.2 cm for GCSB, CSB, MFC, GGB,GB, GMFC, WF, and GWF, respectively. Prior to testing, the speci-mens were sterilized by Portable Auto Claves (Tuttnauer, TM-328)at a temperature of 100e121 �C for 15 min.

2.2. Determination of specific surface area and total pore volume

Specific surface area and total pore volume of samples wereobtained by BrunauereEmmetteTeller (BET) method using BEL-SORP analysis software. Each sample was analyzed by automaticspecific surface area/pore size distribution and chemisorptions in-strument (BELSORP-miniⅡ). The principle of the measurement isbased on gas volume absorbed on solid surface of samples. Specificsurface area and porosity of sample were determined by analyzingthe capacity of absorbing liquid nitrogen gas via solid surface.Sample was degassed at 105 �C for 2 h before sample analysis inorder for BELPREP- flow II to remove the water molecules on thesample surface. Then, each treated sample of 0.2 g wasmeasured bymicrobalance and then poured into a special glass tube. In the end,each sample in the special tube was analyzed by BELSORP-mini IIoperation.

2.3. Water-holding capacity

The water-holding capacity (WHC) of each material was deter-mined by submerging specimens (sized 5 cm � 5 cm) into wateruntil fully saturated. The WHC of the samples was estimated by Eq.(1).

WHC ¼�Mfinal �Minitial

�

Minitial� 100% (1)

Where WHC is the water-holding capacity (%); Minitial is the initialmass of dry material (g) and Mfinal is the mass of fully saturatedmaterial (g). All measurements were in triplicate. The mean andstandard deviation values were calculated.

2.4. Fungal species

Freezed-dried strains of A. brasiliensis (BCRC 31512) and P.funiculosum (BCRC 30438) were purchased from BioresourceCollection and Research Center (BCRC) in Taiwan. They were acti-vated followed the description in the BCRC product instructionsheet before use. After being activated, each of the culture wastransferred to the different potato dextrose agar plate and thenincubated in incubation chamber at a temperature of 28e30 �C and85% RH for 14 days in preparation of two spore suspensions. Theconcentration of A. brasiliensis spores in the first suspension wasaround 2 � 106 CFU/mL, and the concentration of P. funiculosumspores in the second suspension was also around 2 � 106 CFU/mL.

2.5. Inoculation of test specimens without nano-metals

A volume of 3 mL of each spore suspension was sprayed ontoone surface of each test specimen in triplicate by using an airbrushattached to a mini-compressor with a pressure regulator withwater separator. The non-inoculated area of the material surfaceserved as a negative control area. The inoculated samples were thenplaced in petri dishes covered with a lid and finally incubated in

Table 1Basic composition and density of test materials.

Indoor application Material Composition Density (g/cm3)

Flooring Wooden flooring Wood, plywood, others 0.50Flooring Green wooden flooring Wood, plywood, others 0.59Cabinetry Gypsum board Gypsum (>90%), paper (<5%), others 0.75Cabinetry Green gypsum board Gypsum (>90%), paper (<5%), others 0.73Cabinetry Calcium silicate board Silicate material (61e65%), calcium carbonate (23e29%), organic and inorganic fibers 1.08Cabinetry Green calcium silicate board Silicate material (61e65%), calcium carbonate (23e29%), organic and inorganic fibers 1.21ceiling Mineral fiber ceiling Mineral fiber (88.8%), binder (6%), moistureproof agent (3%), others 0.32ceiling Green mineral fiber ceiling Mineral fiber (88.8%), binder (6%), moistureproof agent (3%), others 0.33

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127 121

incubation chamber at a temperature of 28e30 �C and 85% RH for35 days. In comparison with JIS Z 2911 and ASTM G21-09 methodswhich do not simulate high humidity (e.g. soaked inwater) and theincubation period is only up to 28 days, all specimens in this studywere soaked in water for 4 h first and then put into incubationchamber at a temperature of 28e30 �C and 85% RH for 35 days formold growth observation. The A. brasiliensis or P. funiculosumgrowth on each sample was visually evaluated according to therating scale described in ASTM G21-09 shown in Table 2.

2.6. Inoculation of test specimens with nano-metals

Single kind of nano-metal of Ag (AL-576832-5G, 99.5% particlesize <100 nm), Cu (AF-45504-5G, APS 20e40 nm 99.9%), or Zn (AL-578002-5G, particle size <50 nm) was dissolved in distilleddeionized water. Due to the limitation required by Toxicity char-acteristic leaching procedure according to NIEA R201.14C in Taiwan,the heavy metals including Ag and Cu leached from all greenbuilding material shall not exceed 0.05 mg/L and 0.15 mg/L. Thus,the prepared nano-metals solution were 0.01 g/L, 0.02 g/L, and0.03 g/L for nano-Ag, and 0.05 g/L, 0.08 g/Land 0.10 g/L for nano-Cu.In the meantime, the prepared nano-Zn solution was higher withthe values of 0.05 g/L, 0.15 g/L, 0.30 g/Land 0.60 g/L since there is noapplicable restriction. The resultant solutionwas stirred towell mixfor 2 h. After that, each material specimen in triplicate was soakedin each of the above prepared nano-metals solution by impregna-tion combined with ultrasonic cleaner (DELTA-DC400) for 30 min.Then, each material specimen soaked in nano-metals solution wastaken out to dry for 10 min and placed in petri dishes.

A volume of 3 mL of each spore suspension was sprayed ontoone surface of each test specimen in triplicate by using an airbrushattached to a minicompressor with a pressure regulator with waterseparator. The non-inoculated area of thematerial surface served asa negative control area. Each specimen in a petri dish was thencovered with a lid and finally incubated in incubation chamber at atemperature of 28e30 �C and 85% RH for 35 days. The A. brasiliensisor P. funiculosum growth on each sample was visually evaluatedaccording to the rating scale described in ASTM G21-09 shown inTable 2.

2.7. Validation of ratings

The fungi growth assessment above is somewhat subjective to

Table 2Level of fungi growth ratings on specimens.

Observed growth on specimens (Sporulating or non-sporulating, orboth)

Rating

Traces of growth (less than 10%) 1Light growth (10e30%) 2Medium growth (30e60%) 3Heavy growth (60% to complete coverage) 4(ASTM G21-09:American Society for Testing and Materials)

evaluate the extent of fungi. Numerical values cannot be obtainedbased on human judgment. Thus, cells on each material specimenonwhich fungi growth has been assessed according to Table 2 werecounted by a Hemocytometer (MARIENFELD, 0.0025 mm2, Ger-many). Cells counting on each kind material specimen for eachrating judged by human were averaged and the standard deviationwas provided as well.

3. Results and discussion

3.1. Physical properties of test materials

In Table 3, the results show that CSB and GCSB had the highestspecific surface area and total pore volume. Conventional and cor-responding green pairs had similar specific surface area and totalpore volume. However, specific surface area values between MFCand GMFC and total pore volume values between GB and GGBshowed significant variations. CSB and GCSB had the slightly lowerWHC values (about 60%). MFC, GMFC, GB, GGB,WF and GWF all hadessentially similar level of WHC, comparable to the WHC valuesmeasured by Hoang et al. [23] for bamboo flooring, gypsum board,drywall, inorganic ceiling tile and particle board. High pore volumeis beneficial for oxygen transport, high WHC is easy to hold waterneeded for fungi growth and high surface area is good for fungiattachment.

3.2. Inoculation of test specimens without nano-metals

A. brasiliensis and P. funiculosum cells counting on each kindmaterial specimen for each rating was shown in Table 4. Averagecells counting of A. brasiliensis at rating 1 to 4 on all test materialsare increasing and they are 6.81 � 108/m3, 1.69 � 109/m3,2.39 � 109/m3 and 3.66 � 109/m3, respectively. Average cellscounting of P. funiculosum at rating 1 to 4 on all test materials arealso increasing and they are 6.72 � 108/m3, 1.43 � 109/m3,2.12 � 109/m3 and 3.02 � 109/m3, respectively. Thus, it is suggestedthat the fungi growth assessment by human judgment is reason-able. However, cells counting at same rating varied among differentmaterials. This may be explained by different physical properties ofmaterials themselves.

After being incubated in incubation chamber at a temperature of28e30 �C and 85% RH for 35 days, fungal growth at rating 2 wasobserved on the non-inoculated surface area of GWF and GGB.Slight fungal growth at rating 1 was observed on the non-inoculated surface area of WF and GB (Fig. 1). After being artifi-cially inoculated the A. brasiliensis or P. funiculosum and incubatedin chamber for 35 days, almost all building materials showedP. funiculosum growth at rating 4 after 28 days (Fig. 2). ExtensiveP. funiculosum growth at rating 4 was observed on GMFC, GB, GWF,MFC, WF, GGB, CSB and GCSB after 16, 17, 18, 19, 26, 27, 27 and 28days, respectively. It seems that green materials were not neces-sarily more resistant, nor more prone to fungal growth than their

Table 3Physical properties of test materials.

Material Specific surface area (m2/g) Total pore volume (cm3/g) Water-holding capacity (%)

WF 8.18 � 10�2 ± 1.11 � 10�2 2.38 � 10�3 ± 0.01 � 10�3 83.2 ± 0.6GWF 8.24 � 10�2 ± 0.91 � 10�2 2.46 � 10�3 ± 0.01 � 10�3 80.3 ± 0.7GB 1.11 ± 0.03 2.33 � 10�2 ± 0.02 � 10�2 71.3 ± 0.5GGB 1.29 ± 0.05 7.66 � 10�2 ± 0.05 � 10�2 76.3 ± 0.5CSB 27.25 ± 0.12 0.29 ± 0.02 59.6 ± 0.4GCSB 34.87 ± 0.26 0.29 ± 0.02 60.2 ± 0.4MFC 6.46 ± 0.031 3.14 � 10�2 ± 0.03 � 1 0�2 80.3 ± 0.6GMFC 1.12 ± 0.014 2.12 � 10�2 ± 0.02 � 10�2 83.0 ± 0.6

Note: Results are shown as the mean value ± standard deviation. “WF” refers to wooden flooring; “GB refers to gypsum board; “CSB” refers to calcium silicate board; “MFC”refers to mineral fiber ceiling; “GWF” refers to green wooden flooring; “GGB” refers to green gypsum board; “GCSB” refers to green calcium silicate board; “GMFC” refers togreen mineral fiber ceiling.

Table 4Cells counting on each kind material specimen for each rating.

Fungal Rating BM

WF GWF GB GGB CSB GCSB MFC GMFC Average cells counting (#/m3)

Cells (#/m3)

A 1 7.75 * 108 7.25 * 108 5.75 * 108 6.50 * 108 1.13 * 109 9.75 * 108 3.25 * 108 3.00 * 108 6.81 * 108

2 2.03 * 109 1.98 * 109 1.45 * 109 1.28 * 109 2.13 * 109 1.90 * 109 1.28 * 109 1.53 * 109 1.69 * 109

3 3.00 * 109 2.73 * 109 2.23 * 109 1.88 * 109 2.30 * 109 1.98 * 109 2.45 * 109 2.55 * 109 2.39 * 109

4 3.55 * 109 3.30 * 109 3.53 * 109 3.03 * 109 3.78 * 109 4.20 * 109 4.03 * 109 3.85 * 109 3.66 * 109

P 1 5.75 * 108 7.50 * 108 7.75 * 108 9.00 * 108 9.75 * 108 7.25 * 108 3.00 * 108 3.75 * 108 6.72 * 108

2 8.75 * 108 1.03 * 109 1.68 * 109 1.78 * 109 2.03 * 109 1.73 * 109 1.03 * 109 1.28 * 109 1.43 * 109

3 1.98 * 109 2.23 * 109 2.48 * 109 2.40 * 109 2.23 * 109 1.98 * 109 1.70 * 109 1.95 * 109 2.12 * 109

4 2.63 * 109 3.03 * 109 3.28 * 109 3.20 * 109 3.40 * 109 3.30 * 109 2.28 * 109 3.03 * 109 3.02 * 109

Note: “A” refers to Aspergillus； “P” refers to Penicillium.

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127122

conventional counterparts, consistent with the findings of Hoanget al. [23]. Moreover, A. brasiliensis grows faster than P. funiculosumgiven A. brasiliensis growth at rating 2 after only 7 days and growthat rating 4 after 25 days (Fig. 3). Extensive A. brasiliensis growth atrating 4 was observed on MFC, GWF, GMFC, WF, GGB, CSB, GB andGCSB after 11,15, 21, 23, 24, 24, 25 and 25 days, respectively. Thus, itseems that MFC, GMFC, WF and GWF have faster fungal growththan GB, GGB, CSB and GCSB.

3.3. Inoculation of test specimens with nano-Silver

After being soaked in nano-silver solution (with concentrationsof 0.01 g/L, 0.02 g/L and 0.03 g/L) and inoculated the A. brasiliensisor P. funiculosum, the fungal growth on each of test material for 35days were shown in Supplementary material. In general, nano-silver used in this study failed to provide complete protection

Fig. 1. Fungal growth on non-inoculated surface area of building materials.

against fungal growth on the eight test building materials at theselected concentrations. However, the higher the nano-metalconcentration was, the longer the lag period until growth beganand less fungi grew on the materials.

For nano-silver concentration of 0.01 g/L, there was noP. funiculosum growth during the first four days and noA. brasiliensis growth during the first two days. Fungal growth atrating 1 and rating 2 were observed on all test materials within 6days and 20 days, respectively. Growth of P. funiculosum on GB andA. brasiliensis on GMFC, GB, GGB,WF stayed at rating 2 after 35 days.For nano-silver concentration of 0.02 g/L, there was no fungalgrowth during the first four days. Fungal growth at rating 1 andrating 2 were observed on all test materials within 6 days and 17days, respectively. Growth of P. funiculosum on WF, GB, GGB andA. brasiliensis on GMFC, GB, GGB,WF, MFC stayed at rating 2 after 35days. For nano-silver concentration of 0.03 g/L, there was no fungal

Fig. 2. Growth of Penicillium on building materials without nano-metals.

Fig. 3. Growth of Aspergillus on building materials without nano-metals.

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127 123

growth during the first seven days. In addition, no fungal growth atrating 4 was observed on any test material. Fungal growth at rating1 was observed on all test materials within 6 days. Growth ofP. funiculosum on GCSB, GMFC, WF, CSB and A. brasiliensis on MFC,GMFC, GB and GGB stayed at rating 1 after 35 days.

Fungal growth ratings for building materials impregnated withnano-silver after 35 days were shown in Tables 5 and 6. For Peni-cillium growth on materials with nano-silver, the results showedimproved fungal growth resistance on all test materials relative tocontrol tests. Resistance to Penicillium growth on GWF was notenhanced obviously at the selected concentrations of nano-silver inthis work (Table 5). For Aspergillus growth on materials with nano-silver, improved fungal growth resistance was also observed on alltest materials relative to control tests. Resistance to Aspergillusgrowth on GWF was not enhanced obviously, similar to the resultsfor Penicillium. However, Aspergillus growth on CSB and GCSB wasnot significantly inhibited (Table 6).

3.4. Inoculation of test specimens with nano-Copper

After being soaked in nano-copper solution (with concentra-tions of 0.05 g/L, 0.08 g/L and 0.1 g/L) and inoculated theA. brasiliensis or P. funiculosum, the fungal growth on each of testmaterial for 35 days were shown in Supplementary material. Ingeneral, nano-copper used in this study failed to provide completeprotection against fungal growth on the eight test building mate-rials at the selected concentrations. However, the higher the nano-metal concentration was, the longer the lag period until growthbegan and fewer fungi grew on the materials.

For nano-copper concentration of 0.05 g/L, there was noP. funiculosum growth during the first three days and noA. brasiliensis growth during the first four days. Fungal growth at

Table 5Penicillium growth ratings on building materials impregnated with nano-metals after 35

Nano-metals Concentration (g/L) WF GWF G

Control N/A 4 4 4Ag 0.01 3 4 2

0.02 2 3 20.03 1 3 2

Cu 0.05 2 4 20.08 2 3 10.10 1 2 1

Zn 0.05 3 4 20.15 2 4 30.30 1 3 20.60 1 2 1

rating 1 was observed on all test materials within 6 days. Growth ofP. funiculosum on GGB, MFC and A. brasiliensis on WF stayed atrating 1 after 35 days. For nano-copper concentration of 0.08 g/L,there was no fungal growth during the first four days. Fungalgrowth at rating 1 was observed on all test materials within 7 days.Growth of P. funiculosum on GGB, GB and A. brasiliensis on WFstayed at rating 1 after 35 days. For nano-copper concentration of0.1 g/L, there was no fungal growth during the first four days.Fungal growth at rating 1 was observed on all test materials within6 days. Growth of P. funiculosum onWF, GB and A. brasiliensis onWFstayed at rating 1 after 35 days.

Fungal growth ratings for building materials impregnated withnano-copper after 35 days were shown in Tables 5 and 6. ForPenicillium growth on materials with nano-copper, the results onlyshowed improved fungal growth resistance on WF, GWF, GB andGGB relative to control tests, while no significant fungal resistanceeffect of nano-copper was observed on CSB, GCSB, MFC and GMFCat the selected concentrations of nano-copper in this work(Table 5). For Aspergillus growth on materials with nano-copper,improved fungal growth resistance ability was observed on alltest materials relative to control tests. Thus, it seems that nano-copper works better to resist Aspergillus than Penicillium on CSB,GCSB, MFC and GMFC (Table 6).

3.5. Inoculation of test specimens with nano-Zinc

After being soaked in nano-zinc solution (with concentrations of0.05 g/L, 0.15 g/L, 0.30 g/L and 0.60 g/L) and inoculated theA. brasiliensis or P. funiculosum, the fungal growth on each of testmaterial for 35 days were shown in Supplementary material. Ingeneral, nano-zinc used in this study failed to provide completeprotection against fungal growth on the eight test building mate-rials at the selected concentrations. However, the higher the nano-metal concentration was, the longer the lag period until growthbegan and fewer fungi grew on the materials.

For nano-zinc concentration of 0.05 g/L, there was no fungalgrowth during the first three days. Fungal growth at rating 1 and 2were observed on all test materials within 6 days and 18 days,respectively. Growth of P. funiculosum on GB stayed at rating 2 after35 days. For nano-zinc concentration of 0.15 g/L, there was nofungal growth during the first three days. Fungal growth at rating 1and 2were observed on all testmaterials within 6 days and 27 days,respectively. . Growth of P. funiculosum on WF and A. brasiliensis onGCSB, CSB, GB and WF stayed at rating 2 after 35 days. For nano-zinc concentration of 0.30 g/L, there was no fungal growth duringthe first three days. Fungal growth at rating 1 was observed on alltest materials within 8 days. Growth of P. funiculosum on MFC, WFstayed at rating 1 after 35 days. For nano-zinc concentration of0.60 g/L, there was no fungal growth during the first seven days.Fungal growth at rating 1 was observed on all test materials within

days.

B GGB CSB GCSB MFC GMFC

4 4 4 4 43 3 3 4 32 4 3 4 42 1 1 1 11 4 4 1 31 4 4 4 42 4 4 4 43 4 3 4 33 3 3 3 33 2 2 1 31 1 2 2 3

Table 6Aspergillus growth ratings on building materials impregnated with nano-metals after 35 days.

Nano-metals Concentration (g/L) WF GWF GB GGB CSB GCSB MFC GMFC

Control N/A 4 4 4 4 4 4 4 4Ag 0.01 2 4 2 2 4 3 4 2

0.02 2 3 2 2 4 3 2 20.03 2 3 1 1 3 3 1 1

Cu 0.05 1 3 2 2 3 3 4 30.08 1 4 2 2 3 3 2 40.10 1 2 2 3 2 2 2 2

Zn 0.05 3 4 3 3 3 3 4 40.15 2 4 2 3 2 2 4 40.30 2 3 2 2 2 2 4 40.60 1 2 1 1 1 1 4 4

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127124

18 days. Growth of P. funiculosum on GGB, WF, CSB, GB andA. brasiliensis on GCSB, WF, CSB, GGB and GB stayed at rating 1 after35 days.

Fungal growth ratings for building materials impregnated withnano-zinc after 35 days were shown in Tables 5 and 6. For Penicil-lium growth on materials with nano-zinc, the results showedimproved fungal growth resistance on all test materials relative tocontrol tests. Resistance to Penicillium growth on GMFC was notenhanced obviously (Table 5). For Aspergillus growth on materialswith nano-zinc, improved fungal resistance was observed on alltest materials except MFC and GMFC (Table 6).

4. Discussion

The results of building material inoculation without nano-metals showed that MFC, GMFC, WF and GWF had faster fungalgrowth than GB, GGB, CSB and GCSB, probably due to their greaterWHCs which help the materials absorb water very fast, leading tofaster mold growth. In addition, MFC, GMFC, WF and GWF maywork as better organic food sources that provide necessary nutri-tion for fungal growth [23,30,31].

Average fungal ratings for test building materials treated withnano-metals at the highest selected concentrations after 35 dayswere shown in Figs. 4e7. It can be seen that fungi grew at similarrates on green building materials relative to their conventionalcounterparts treated by nano-metals except that a lot more fungiwere found on GWF than WF treated by any nano-metals in thisstudy. A bit more fungi grew on GGB, GCSB and GMFC than theirconventional counterparts treated by nano-copper, nano-zinc andnano-zinc, respectively. Thus, although the fungi growth withoutnano-metals on test materials in this work did not show that greenmaterials were more prone to fungal growth, they were lessresistant to fungi attack relative to their conventional counterpartstreated by nano-metals. The reason may be related to differentinteractions between green materials and nano-metals, leading tomore fungal growth, which needs further study to identify. It is also

Fig. 4. Average fungal ratings for MF and GWF treated with nano-

demonstrated that the order of fungal growth resistance of nano-metals at their highest selected concentrations in this study ontest materials was nano-zinc ¼ nano-copper > nano-silver for WFand GWF, nano-zinc > nano-silver ¼ nano-copper for GB, nano-zinc > nano-silver > nano-copper for GGB, CSB and GCSB, nano-silver > nano-copper¼ nano-zinc for MFC, and nano-silver > nano-copper > nano-zinc for GMFC.

Thus, for WF, GWF, GB, GGB, CSB and GCSB, nano-zinc is themost promising nano-metal to help protect them from fungi attack.Both Mantanis et al. [47] and Kartal et al. [42] used nano-zinc andnano-copper to evaluate termite and mold resistance on pinewoodand wood. Their findings suggested that nano-zinc is more favor-able in terms of leach resistance, termite mortality and inhibition oftermite feeding and decay by the white-rot fungus. In addition,nano-zinc is the cheapest among the three nano-metals and itsconcentration is not limited by Toxicity characteristic leachingprocedure according to NIEA R201.14C in Taiwan. Therefore, itseems that nano-zinc is the most favorable nano-metal for woodand wood composite materials. As for MFC and GMFC, nano-silverseems better to help resist fungal growth than the other two nano-metals in this work.

5. Conclusions

Although the fungi growth without nano-metals on test mate-rials in this work did not show that green materials were moreprone to fungal growth, they were less resistant to fungi attackrelative to their conventional counterparts treated by nano-metals,especially GWF and WF. All test nano-metals in this study failed toprovide complete protection against fungal growth on the eight testbuilding materials at the selected concentrations. However, thehigher the nano-metal concentrationwas, the longer the lag perioduntil growth began and fewer fungi grew on the materials. Nano-zinc seems to be the most favorable nano-metal for wood andwood composite materials in this study.

Only four conventional and their green pair materials in Taiwan

metals at the highest selected concentrations (after 35 days).

Fig. 5. Average fungal ratings for GB and GGB treated with nano-metals at the highest selected concentrations (after 35 days).

Fig. 6. Average fungal ratings for CSB and GCSB treated with nano-metals at the highest selected concentrations (after 35 days).

Fig. 7. Average fungal ratings for MFC and GMFC treated with nano-metals at the highest selected concentrations (after 35 days).

H.-L. Huang et al. / Building and Environment 93 (2015) 119e127 125

were tested, further researches are needed to evaluate a biggerrange of green and conventional building materials. It is beneficialto better understand the mechanisms of nano-metals affectingfungal growth on both green materials and their conventionalcounterparts. In addition, it may be desirable to identify in-teractions between green materials and nano-metals, leading tomore fungal growth, which needs further study to identify mainfungal species that grow on various building materials and toevaluate their growth and deterioration resistance on these mate-rials treated with nano-metals. This study will provide useful in-formation for comparing the green and conventional materials interms of fungal growth resistance before and after nano-metaltreatment. It also helps choose best nano-metals to improvefungal resistance of buildings materials.

Acknowledgments

The authors would like to thank Ministry of Science and Tech-nology of the Republic of China for funding this research (under

contract MOST 100-2221-E-390-002 and MOST 101-2221-E-390-010-MY3). We also wish to thank Dr. Ping Zhao for the help ofEnglish editing.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.buildenv.2015.06.016.

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