Development of Nano TiO2–Geopolymer Functional Composite as Antifouling Bricks

The purpose of study is to examine the ability of nano TiO2 – geopolymer functional composite as antifouling bricks. The samples were synthesized through alkali-activation method at 70C for 1 hour by mixing metaclay with TiO2 nanoparticles and activated with sodium silicate solution. There were two series of samples produced, namely, GT_A with addition of 2% nanoTiO2 and GT_B with addition of 4% nano TiO2 relative to the mass of metaclay. The samples were immersed in water and in 1M H2SO4 solution for 4 days to examine the resistance of composites in hars environment. The x-ray diffraction (XRD) was performed to examine the chemical compositions of the samples before and after environmental test. The morphology of the samples surfaces was examined by using Scanning Electron Microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Based on this study, sample GT_A shows its excellent properties as antifouling bricks. The addition of nano TiO2 was found to improve the quality of geopolymers as a high performance bricks.


Introduction
Brick is one of construction materials that have been known by people around the world, both in rural and urban areas.Conventionally, manufacture of bricks need to be burned and dried (traditional bricks) and it may cause air pollution in the surrounding environment [1][2]19].Traditional bricks as a raw material in the building are vulnerable to weathering both chemically and mechanically, brittle and sensitive to the salting reaction, and directly related to the presence of micro-organisms deposit on the building [3][4][5][20][21].Biofouling can be defined as the accumulation of micro-organisms, plants, and animals which are attached to either temporary or permanent on building facades [6].One of the promising material which has abundant precursor and easy to produce is geopolymer bricks.
Geopolymer was developed by Davidovits in the late 1978, synthesized through polycondensation of aluminosilicate minerals (e.g., metakaolin, clay, fly ash) with a solution of alkali (e.g., sodium hydroxide and sodium silicate) [7][8][9].Many researchers use clay as raw material for manufacturing geopolymer for bricks application [10][11].The most important advantages of geopolymer bricks are resistance to acid attack, high early strength, long-term durability, good fire resistance, low manufacturing energy consumption, and low CO 2 emission, which make these novel material to be categorized as "green material" [11][12][13][14].Recently, the latest innovation that provides added value to the geopolymer bricks is to incorporate anti-fungal or anti biofouling material.
Nanomaterials are increasingly developed due to its size (1-100 nanometers) in at least one dimension.Their physical and chemical properties differ from those of bulk materials (controlling matter at atomic level).It can be used as prevention of building materials from organic contamination.Titanium dioxide (TiO 2 ) is one of the most used material to realize self-cleaning and its general use is attributed to its main features: high catalysis efficiency and chemical stability, inexpensiveness, compatibility with traditional construction [15].The advantage of using TiO 2 as follows: (i) protective or anti corrosion coating mechanism; (ii) thermal control; (iii) easy to clean; (iv) anti bacterial coating for work surfaces; (v) anti grafitti coating for building and structure, (vi) low-cost [16,17].Furthermore, the most importance of nano-TiO 2 is its inert properties, corrosion resistance due to light or chemicals and non-toxic [18].
This study utilizes clay-based geopolymer as the raw material forming the matrix of geopolymer and nano TiO 2 as antifouling agent.This study was carried out to determine the quality and capability of functional composite nano TiO 2 -geopolymer as antifouling bricks.

Experimental
This study is a development research that lead to the development of Nano TiO 2geopolymer as antifouling bricks through alkaline-activation method.Metaclay was produced from calcined clay at 750 0 C for 6 hours as a source of aluminosilicate and TiO 2 (anatase) as antifouling agent (filler).The alkaline solution for geopolymerization was a mixture of sodium hydroxide (NaOH), sodium silicate (Na 2 O.3SiO 2 ) and distilled water (H 2 O) with a certain concentration.Geopolymer bricks was produced by mixing the basic ingredients of the metaclay with nano TiO 2 and activated with an alkaline solution to obtain a homogeneous paste.
Geopolymer paste was poured into the block-shaped glass mold with size 20 cm x 8 cm x 4 cm and then cured in an oven at 70 0 C for 1 hour.After the age of 24 hours, the samples were removed from the mold and tested after 3 days.After the age of 7 days, the samples were immersed in water solution and sulfuric acid (H 2 SO 4 1 M).The physical properties (pH levels, bulk density, mass, and colour change) were monitored daily.Durability test have been performed to the geopolymer bricks containing Nano TiO 2, which consist of acid attack and environment test.Samples which have been tested were characterized by XRD to examine the structure of the samples.SEM characterization was used to study the structure and morphology of the sample before and after testing.

Results and discussions
After the age of 7 days, Nano TiO 2 -Geopolymer samples were tested.Each sample was immersed in solutions of sulfuric acid (H 2 SO 4 1 M) and water for 4 days.Table 1 below shows the value of bulk density of each sample before and after testing.Sample geopolymer without nano-TiO 2 was produced by Riska [22] with an average composite strength 58.44 MPa.This research focused on the mechanical strength.Figure 1 shows the appearance of (a) GT_A (b) GT_B before acid attack and environment test of each sample.In this study, clay is used as raw material due to its abundant availability in South Sulawesi, Sidrap Regency, Indonesia.Table 2 shows the composition of clay raw material.Based on XRF analysis, it can be shown that the main oxide composition of clay were SiO 2 , Al 2 O 3 , and Fe  Figure 3a shows the XRD pattern of meta-clay that has a certain crystalline structure with the highest peak lies between 25 0 -27 0 (2θ).The XRD analysis shows that the main compositions of meta-clay were SiO 2 in the form of quartz, magnetite and hematite.Figure 3b shows the characterization results of the Nano TiO 2 and all the peaks can be indexed as anatase form of TiO 2 (the average particle size is 12 nm).Phase characterization shows that the most dominant peaks both of GT_A and GT_B lies between 20 0 -30 0 (2θ) which consist of quartz, almandite, magnetite, hematite, rutile, sodium calcium-cyclo hexasilicate joining with anatase.Overall, there is no significant change due to the addition of nano TiO 2 in geopolymer structure.Table 2 shows the chemical composition of the phase of nano TiO 2 -geopolymer (in wt%).Figure 5a shows the diffraction pattern of the sample after acid attack and Fig. 5b shows the diffraction pattern of the sample after environmental test.Phase characterization shows that the most dominant peaks both of GT_A and GT_B after acid attack lies between 27 0 -30 0 (2θ) which consist of quartz, almandine, magnetite, hematite, rutile, sodium calcium-cyclo hexasilicate and anatase.Figure 5b shows that all samples consist of quartz, anatase, rutile, hematite, with addition of sodium dialuminium-phyllo decaoxodihydroxo allumotrisilicate and favalite.Similarly, its diffractogram shows that the most dominant peaks after environment test lies between 27 0 -30 0 (2θ).6a and 6b; (ii) after acid attack is shown in Fig. 6c and 6d; (iii) and after environmental test is shown in Fig. 6e.It is well known that nano TiO 2 with particle size below 500 nm, can strongly bonded in geopolymer although it was attacked by strong acid solution and hars enviromental [20].In addition, the most commonly used oxide is the anatase form of TiO 2 , which for practical reason of safety and easily for handling and encapsulated in an inorganic matrix [16][17][18][19].The chemical composition of each sample before and after acid attack testing is presented in Table 3.

Summary
Functional composite of nano TiO 2 -geopolymers have been succesfully synthesized from a mixture of meta-clay with nano TiO 2 through alkali-activation method at 70 0 C for 1 hour.The addition of nano TiO 2 improved the quality of geopolymer to resist acid attack and hars environment.Based on this research, sample containing 2% nano TiO 2 shows excellent properties as antifouling bricks.

Fig. 1 .
Fig. 1. (i) The appearance of : (a) MC + 2% NanoTiO 2 ; (b) MC + 4% NanoTiO 2 before acid attack, (ii) The appearance of (c) MC + 2% NanoTiO 2 ; (d) MC + 4% NanoTiO 2 before environmental test The appearances of each sample before and after testing in strong acid solution 1 M H 2 SO 4 and water for 4 days were shown clearly in Figure 2. It can be explained that there are physical change and densification after immersing in acid solution.

Fig. 3 .Figure 4
Fig. 3. Phase characterization of (a) metaclay; (b) nano TiO 2 Figure 4 is the result of phase characterization of sample namely GT_A with addition of 2% nano TiO 2 relatively to its precursor mass and GT_B with addition of 4% nano TiO 2 .The diffraction pattern shows the sample maintain its level of crystallinity.

Fig. 6 .
Fig. 6.SEM images of (a) GT_A; (b) GT_B after acid attack; (c) GT after environment testing Fig.6 clearly shows the SEM image of geopolymers surface displaying the presence of nano TiO 2 represented with white spots.The microstructure of samples, (i) before testing is shown in Fig.6a and 6b;(ii) after acid attack is shown in Fig.6c and 6d;(iii) and after environmental test is shown in Fig.6e.It is well known that nano TiO 2 with particle size below 500 nm, can strongly bonded in geopolymer although it was attacked by strong acid solution and hars enviromental[20].In addition, the most commonly used oxide is the anatase form of TiO 2 , which for practical reason of safety and easily for handling and encapsulated in an inorganic matrix[16][17][18][19].The chemical composition of each sample before and after acid attack testing is presented in Table3.

Table 1 .
The Apparent Porosity and Bulk Density before and After Testing

Table 2 .
Composition of Clay as Raw Material Based on XRF Result

Table 4 .
Chemical composition of Nano-TiO 2 -Geopolymer before and after acid attack test based on EDS result