Thesis Summary
Synthesis, Properties of Graphene Oxide, Graphene Oxide Quantum Dots, and Its
Composite: A Cesium Detector for Environmental Monitoring(㓟໬ࢢࣛࣇ࢙ࣥࠊ㓟໬ࢢࣛࣇ࢙ࣥ㔞Ꮚࢻࢵࢺࠊࡑࡢ」ྜయࡢྜᡂ
࡜ᛶ㉁㸸⎔ቃࣔࢽࢱࣜࣥࢢࡢࡓࡵࡢࢭࢩ᳨࣒࢘ฟჾ )        

BANGUN SATRIO NUGROHOThe Fukushima Daiichi Nuclear Power Plant (FDNPP) accident that
occurred in March, 2011, caused a substantial amount of radioactive material s
released to the environment. Among the radioactive materials released to theenvironment, radiocesium ( 134 Cs and 137 Cs) beside radioiodine ( 131 I) is the mostmajor released volatile radionuclide having a direct impact on land contamination.
The radioactivity can be measured using radiation measurement techniques. In thepresent PhD thesis, I tried to capture radiocesium and also tried to form a cesium
detection system. Background and objective of research are given in detail inChapter 1.
Chapter 2 shows the Exploration of the Cs Trapping Phenomenon byCombining Graphene Oxide with α-K 6 P 2 W 18 O62 as Nanocomposite. Graphene oxide(GO) surface has an interesting interaction using a polar -COO(H) and non-polar(-CH3) group in order to adsorb different kinds of cations (charge, size, complexingcapability) by a proposed ion-bridging mechanism. In addition, Polyoxometalates(POMs) provide an excellent, robust, and discrete material, which has reversible
multi-electron redox properties. Some researchers have employed POMs as apotential Cs adsorption material by using a cation exchange mechanism.
Considering the tremendous properties of GO and α-K 6 P 2 W 18 O 62 , it is highly
desirable to synthesize a new nanocomposite with Cs adsorption ability using theGO and POMs. In this chapter, two types of GO samples were employed. One is GO,
which has a large amount of carbon (C), and the other is GO, which has a large
amount of oxygen (O). They have a variant sp 2 /sp 3 structure. These GOs can beproduced by controlling the oxidation degree, which depends on several factors suchas the reaction condition, oxidizing agent, and graphite source. It has been known
that the GO structure is not precisely determined because of a variety of local

I investigated the interaction of Cs + with the nanocomposite by characterizing thesurface structure of the composite material and also by considering the adsorption
capacity of the nanocomposite for radioactive Cs. Each property in each material isexpected to synergistically strengthen the adsorption capacity of the nanocomposite. A
high Cs adsorption capacity was clearly achieved by using the nanocomposite.
Chapter 3 shows the improvement of Cs detection performance and formationof CsCl and Cs nanoparticles by tuning graphene oxide quantum dot -based
nanocomposite. In recent years, graphene oxide (GO) and graphen e oxide quantum
dots (GOQDs) are widely studied in several applications such as metal adsorbent (Cs + ,Eu 3+ , Sr 2+ ), and designed as fluorescence probes by considering their quantum
confinement and the edge effect. In addition, the GO and GOQDs have almost s imilar
properties because they have various oxygen functional groups. The functional group
can act as a binding point to synthesize a new nanocomposite to improve theirproperties. Another important thing is that the photoluminescence (PL) of GOQDs was
independent of pH. It means that the emission wavelength does not shift in different
pH condition (only change in the PL intensity). Further investigation also revealed that
the PL of GO has shown a reversible response to ionic strength and pH. The previous
work confirmed that the different number of layers of GO (single and a few layers)
showed different optical responses in various organic solvent. More currently, Yao et al.
have employed graphene quantum dot-based fluorescence sensing as a dual detector of
copper ion (Cu 2+ ) and tiopronin (MPG). They proposed a novel fluorescence turn OFF
for the Cu 2+ detection and turn ON for the tiopronin (MPG) detection. Therefore, tofacilitate the development of a Cs detection system, it is highly desirable to create anew nanocomposite using functionalized graphene oxide quantum dots (GOQDs) withcesium green molecule. In Chapter 3, I produced a new nanocomposite that has theability to recognize Cs in water with different pH conditions (acidic and basiccondition) by considering the turn ON/OFF response.
Chapter 4 shows the general conclusions. The present findings haveprovided the fundamental understanding of specific characteristic an d structural
diversity of GO and its nanocomposite. In particular, the C/O ratio and the GO acidity(influenced by the oxidation debris particle) of the GO sample have significantly
influenced the adsorption capacity, the sensitivity and the accuracy of th e detection
system of the GO-based nanocomposite. It can be used as an entry point to design thestructure and the function system for a new advanced nanocomposite. And, the present
study offers a bridge between GO and other potential materials. Also, this work may
open an application in environmental protection with more deep investigation.