Titania based catalysts for photoreduction of carbon dioxide: Role of modifiers

Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry

Volumn 51, Issue 9-10, 2012, Pages 1263-1283

  Jeyalakshmi, V ^a,b   Mahalakshmy, R ^a   Krishnamurthy, K R ^b   Viswanathan, B ^a,b  

^a THIAGARAJAR COLLEGE   (India)

^b INDIAN INSTITUTE OF TECHNOLOGY MADRAS   (India)

Author keywords

Carbon dioxide photoreduction; Photocatalysts; Photophysical properties; Photoreduction; Solar energy; Titania

Indexed keywords

EID: 84866246271     PISSN: 03764710     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

References (192)

1. Fujishima A, Rao T N & Tryk D A, J Photochem Photobiol C Photochem Rev, 1 (2000) 1
2. Carp O, Huisman C L & Reller A, Prog Solid State Chem, 32 (2004) 33.
3. Fujishima A & Zhang X, CR Chim, 9 (2006) 750.
4. Fujishima A, Zhang X & Tryk D A, Int J Hydrogen Energy, 32 (2007) 2664.
5. Osterloh F E, Chem Mater, 20 (2008) 35.
6. (a) Palmisano G, García-López E, Marcí G, Loddo V, Yurdakal S, Augugliaro V & Palmisano L, Chem Commun, 46 (2010) 7074
7. (b) Li K, Martin D & Tang J, Chinese J Catal, 32 (2011) 879.
8. Seery M K, George R, Floris P & Pillai S C, J Photochem Photobiol A, 189 (2007) 258.
9. Rajeshwar K, Chenthamarakshan C R, Goeringer S & Djukic M, Pure Appl Chem, 73 (2001) 1849.
10. Pengfei Ji, Takeuchi M, Cuong T M, Zhang J, Matsuoka M & Anpo M, Res Chem Intermed, 36 (2010) 327.
11. Yang Y, Zhong H & Tian C, Res Chem Intermed, 37 (2011) 91.
12. Teh C M & Mohamed A R, J Alloys Comp, 509 (2011) 1648.
13. Zaleska & Adriana, Recent Pat Eng, 2 (2008) 157.
14. Fujishima A, Zhang X & Tryk D A, Surf Sci Rep, 63 (2008) 515.
15. Anpo M & Takeuchi M, J Catal, 216 (2003) 505.
16. Hoffmann M R, Martin S T, Chi W & Detlef W, Chem Rev, 95 (1995) 69.
17. Malati M A & Wong W K, Surf Tech, 22 (1984) 305.
18. (a)Usubharatana P, McMartin D, Veawab A & Tontiwachwuthikul P, Ind Eng Chem Res, 45 (2006) 2558
19. (b) Dimitrijevic N M, Vijayan B K, Poluektov O G, Rajh T, Gray K A, He H & Zapol P, J Am Chem Soc, 133 (2011) 3964.
20. Choi W, Termin A & Hoffmann M R, J Phys Chem, 98 (1994) 13669.
21. Colmenares J C, Aramendía M A, Marinas A, Marinas J M & Urbano F, J Appl Catal A, 306 (2006) 120.
22. Bellardita M, Addamo M, Di Paola A & Palmisano L, Chem Phys, 339 (2007) 94.
23. Jacinto Sá, Marcos Fernández-Garcia & Anderson J A, Catal Commun, 9 (2008) 1991.
24. Akpan U G & Hameed B H, Appl Catal A, 375 (2010) 1.
25. Asahi R, Morikawa T, Ohwaki T, Aoki K & Taga Y, Science, 293 (2001) 269.
26. Morikawa T, Asahi R, Ohwaki T, Aoki A & Taga Y, Japan JAppl Phys, 20 (2001) L-561.
27. Valentin C D, Pacchioni G, Selloni A, Livraghi S & Giamello, J Phys Chem B,109 (2005) 11414.
28. Valentin D, Finazzi E, Pacchioni G, Selloni A, Livraghi S, Paganini M C & Giamello E, Chem Phys, 339 (2007) 44.
29. Diwald T L, Thompson T, Zubkovc E G, Goralski S D, Walck S D & Yates J T, J Phys Chem B,108 (2003) 52
30. Diwald, Thompson T L, Goralski E G, Walck S D & Yates J T, Jr, J Phys Chem B, 108 (2004) 6004.
31. Chen X & Burda C, J Phys Chem B, 108 (2004) 15446.
32. Gopinath C S, J Phys Chem B, 110 (2006) 7079.
33. Satish M, Viswanathan B, Viswanath R P & Gopinath C S, Chem Mater, 17 (2005) 6349.
34. Umebayashi T, Yamaki T, Itoh H & Asai K, Appl Phys Lett, 81 (2002) 454.
35. Ohno T, Akiyoshi M, Umebayashi T, Asai K, Mitsui T & Matsumura M, Appl Catal A, 265 (2004) 115.
36. Xu R, Killmeyer R, Gray M L & Khan S U M, Electrochem Commun, 8 (2006) 1650.
37. Li Y, Hwang D S, Lee N H & Kim S J, Chem Phys Lett, 404 (2005) 25.
38. Ho W, Yu J C & Lee S, Chem Commun, 10 (2006) 1115.
39. Li A, Haneda H, Labhsetwar N K, Hishita S & Ohashi N, Chem Phys Lett, 401 (2005) 579.
40. Zaleska A, Grabowska E, Sobczak J W, Gazda M & Hupka J, Appl Catal B, 89 (2009) 469.
41. Chen A, Yang D, Wang Q & Jiang Z, Ind Eng Chem Res, 45 (2006) 4110.
42. Long R & English N J, Chem Mater, 22 (2010) 1616
43. Phys Rev B, 83 (2011) 155209
44. Appl Phys Lett, 94 (2009) 132102.
45. Gao B F, Ma Y, Cao Y A, Yang W S & Yao J N, J Phys Chem B, 110 (2006) 14391.
46. Shen Y F, Xiong T Y, Li T F & Yang K, Appl Catal B, 83 (2008) 177.
47. Lia X, Sib D, Fang J, Jiang Z & Huang W, Chinese J Chem Phys, 19 (2008) 539.
48. Jureka A Z, Kowalska E, Sobczakc J W, Lisowski W, Ohtanib B & Zaleska A, Appl Catal B, 101 (2011) 504.
49. Yang P, Lu C, Hua N & Du Y, Mater Lett, 57 (2002) 794.
50. Tian B, Li C, Gu F & Jiang H, Catal Commun, 10 (2009) 925.
51. Zhang S, Song L, Zhang S, Sun D & Chen B, React Kinet Catal Lett, 97 (2009) 199.
52. Liu G, Zhao Y, Sun C, Li F, Lu G Q & Cheng H M, Angew Chem Int Ed, 47 (2008) 4516.
53. Shao G S, Ma T Y, Zhang X J, Ren T Z & Yuan Z Y, J Mater Sci, 44 (2009) 6754.
54. Special issue on Doping and Functionlization of Photoactive Semiconducting Metal Oxide, edited by C D Valentin, U Diebold & A Selloni, Chem Phys, 339 (2007) pp. 1-192.
55. Huang L, Peng F, Wang H, Yu H & Li Z, Catal Commun, 10 (2009) 1839.
56. Hyun B R, Zhong Y W, Bartnik A C, Sun L, Abruna H D, Wise F W, Goodreau J D, Matthews J R, Leslie T M & Borrelli N F, ACS Nano, 2 (2008) 2206.
57. Wang C, Kwon K W, Odlyzko M L, Lee B H & Shim M, J Phys Chem C, 111 (2007) 11734.
58. Wong C, Thompson R L, Baltrus J & Matranga C, J Phys Chem Lett, 1 (2010) 48.
59. Cho Y, Choi W, Lee C, Hyeon T & Lee H, Environ Sci Technol, 35 (2001) 966.
60. Ross H, Bendig J & Hecht S, Sol Energy Mater Sol Cells, 33 (1994) 475.
61. Mele G, Ciccarella G, Vasapollo G, Garć?a-López E, Palmisano L & Schiavello M, Appl Catal B, 38 (2002) 309.
62. Gratzel M, Inorg Chem, 44 (2005) 6841.
63. Chen C Y, Wang M, Li J Y, Pootrakulchote N, Alibabaei L, Ngoc-le C, Decoppet J D, Tsai J H, Gratzel C, Wu C G, Zakeeruddin S M & M Gratzel, ACS Nano, (2009) DOI: 10 1021/nn900756s.
64. Awazu K, Fujimaki M, Rockstuhl C, Tominaga J, Murakami H, Ohki Y, Yoshida N & Watanabe T, J Am Chem Sci, 130 (2008) 1676.
65. Cláudia Gomes Silva, Juárez R, Marino T, Molinari R & García H, J Am Chem Sci, 133 (2011) 595.
66. Jiun-Jen Chen, Wu J C S, Wu P C & Tsai D P, J Phys Chem C, 115 (2011) 210.
67. WenboHou, Hung W H, Pavaskar P, Goeppert A, Aykol M & Cronin S B, ACS Catal, 1 (2011) 929.
68. Kisch H & Macyk W, Chem Phys Chem, 3 (2002) 399.
69. Morgan B J & Watson G W, J Phys Chem C, 113 (2009) 7322.
70. Roldán A, Boronat M, Corma A & Illas F, J Phys Chem C, 114 (2010) 6511.
71. Suriye K, Praserthdam P & Jongsomjit B, Appl Surf Sci, 253 (2006) 3849.
72. Nakamura I, Negishi N, Kutsuna S, Ihara I, Sugihara S & Takeuchi K, J Mol Catal A: Chem, 161 (2000) 205.
73. Liu G, Wang L Z & Yang H G, J Mater Chem, 20 (2010) 831.
74. Yoneyama H, Catal Today, 39 (1997) 169.
75. Serpone N, Lawless D & Khairutdinov R, J Phys Chem, 99 (1995) 16646.
76. Anpo M & Takeuchi M, J Catal, 216 (2003) 505, Refs 42-56 and 125-140 therein.
77. (a) Anpo M, Yamashita H, Ichihashi Y & Ehara S, J Electroanal Chem, 396 (1995) 21
78. Green J, Carter E & Murphy D M, Chem Phys Lett, 477 (2009) 340
79. (b) Rajalakshmi K, Jeyalakshmi V, Krishnamurthy K R & Viswanathan B, Indian J Chem, 51A (2012) 411.
80. Kumar K N P, Keizer K, Burggraaf A J, Okubo T, Nagamoto H & Morooka S, Nature, 358 (1992) 48.
81. Gopal M, Moberly Chan W J & De Jonghe L C, J Mater Sci, 32 (1997) 6001.
82. Ito S, Inoue S, Kawada H, Hara M, Iwasaki M & Tada H, J Colloid Interface Sci, 216 (1999) 59.
83. Terabe K, Kato K, Miyazaki H, Yamaguchi S, Imai A & Iguchi Y, J Mater Sci, 29 (1994) 1617.
84. Roy S C, Varghese O K, Paulose M & Grimes C A, ACS Nano, 4 (2010) 1259.
85. Indrakanti V P, Kubicki J D & Schobert H H, Energy Environ Sci, 2 (2009) 745.
86. Jiang Z, Xiao T, Kuznetsov V L & Edwards P P, Phil Trans Royal Society A, 368 (2010) 3343.
87. Inoue T, Fujishima A, Konishi S & Honda K, Nature, 277 (1979) 637.
88. Scibioh M A & Viswanathan B, Proc Ind Natl Sci Acad A, 70 (2004) 407.
89. Koci K, Obalova L & Lancy Z, Chem Pap, 62 (2008) 1.
90. (a) Ishitani O, Inoue C, Suzuki Y & Ibusuki T, J Photochem Photobiol A, 72 (1993) 269
91. (b) Dzhabiev T S, Tarasov B B & Uskov A M, Catal Today, 13 (1992) 695.
92. Solymosi F & Klivenyi G, Catal Lett, 22 (1993) 337.
93. Solymosi F & Tombtcz I, Catal Lett, 27 (1994) 61.
94. Rasko J & Solymosi F, J Phys Chem, 98 (1994) 7147.
95. Kohno Y, Hayashi H, Takenaka S, Tanaka T, Funabiki T & Yoshida S, J Photochem Photobiol A, 126 (1999) 117.
96. Willner I, Maidan R, Mandler D, Dum H, Dorr G & Zengerle K, ACS, 109 (1987) 6080.
97. Halmann M, Katzir V, Borgarello V & Kiwi J, J Sol Energy Mater, 10 (1984) 85.
98. Sasirekha N, Basha S J S & Shanthi K, Appl Catal B, 62 (2006) 169.
99. Chandrasekaran K & Thomas J K, Chem Phys Lett, 99 (1983) 7.
100. Goren Z, Willner I & Nelson A J, J Phys Chem, 94 (1990) 3784.
101. Anpo M, Yamashita H, Ichihashi Y, Fujii Y & Honda M, J Phys Chem B, 101 (1997) 2632.
102. Zhang Q-H, Han W D, Hong Y J & Yu J G, Catal Today, 148 (2009) 335.
103. Yui T, Kan A, Saitoh C, Koike K, Ibusuki T & Ishitani O, ACS Appl Mater Interfaces, 3 (2011) 2594.
104. Subrahmanyam M, Kaneco S & Alonso-Vante N, Appl Catal B, 23 (1999) 169.
105. Sasikalaa R, Shirole A R, Sudarsan V, Kamble V S, Sudakar C, Naik R, Rao R & Bharadwaja S R, Appl Catal A, 390 (2010) 245.
106. Koči K, Matěju K, Obalova L, Krejčikova S, LacnýZ, Placha D, Čapek L, Hospodkova A & Solcova O, Appl Catal B, 96 (2010) 239.
107. Sclafani A & Hermann J M, J Photochem Photobiol A, 113 (1998) 181.
108. Iliev V, Tomova D, Bilyarska L, Eliyas A & Petrov L, Appl Catal B, 63 (2006) 266.
109. Asi M A, He C, Su M, Xia D, Lin L, Deng H, Xiong Y, Qui R & Li X, Catal Today, 175 (2011) 256.
110. Wu J C S, Catal Surv Asia, 13 (2009) 30
111. Wu J C S, Wu T-H, Chu T, Huang H & Tsai D, Topics Catal, 47 (2008) 131.
112. Adachi K, Ohta K & Mizuno T, Solar Energy, 53 (1994) 187.
113. Tseng I-H & Wu J C S, Catal Today, 97 (2004) 113.
114. Tseng I-H, Wu J C S & Chou H-Y, J Catal, 221 (2004) 432.
115. Tseng I-H, Chang W-C & Wu J C S, Appl Catal B Environ, 37 (2002) 37.
116. Slamet, Nasution H W, Purnama E, Koesla S & Gunlauardi, J Catal Commun, 6 (2005) 313.
117. Li Y, Wang W, Zhan Z, Woo M, Wu C & Biswas P, Appl Catal B, 100 (2010) 386.
118. Varghese O K, Paulose M, LaTempa T J & Grimes C A, NanoLett, 9 (2009) 731.
119. Fan J, Liu E, Tian L, Hu X, He Q & Sun T, J Environ Eng, 137 (2011) 171.
120. Emeline A V, Kuznetsov V N, Rybchuk V K & Serpone N, Int J Photoenergy, 111, (2008) 8394.
121. Torres G R, Lindgren T, Lu J, Granqvist C G & Lindquest S E, J Phys Chem B, 108 (2004) 5995.
122. Hussain S T, Khan K & Hussain R, J Nat Gas Chem, 18 (2009) 383.
123. Woan K, Pyrgiotakis G & Sigmund W, Adv Mater, 21 (2009) 2233.
124. Tryba B, Int J Photoenergy, (2008) doi:10.1155/2008/721824.
125. Leary R & Westwood A, Carbon, 49 (2011) 741.
126. Park Y, Kim W, Park H, Tachikawa T, Majima T & Choi W, Appl Catal B, 91 (2009) 355.
127. Di Valentin C, Pacchioni G & Selloni A, Chem Mater, 17 (2005) 6656.
128. Chen D, Jiang Z, Geng J, Wang Q & Yang D, Ind Eng Chem Res, 46 (2007) 2741.
129. Sun H, Bai Y, Cheng Y, Jin W & Xu N, Ind Eng Chem Res, 45 (2006) 4971.
130. Tachikawa T, Tojo S, Kawai K, Endo M, Fujitsuka M & Ohno T, J Phys Chem B,108 (2004) 19299.
131. Woan K, Pyrgiotakis G & Sigmund W, Adv Mater, 21 (2009)2233.
132. Faria J L & Wang W, in Carbon Materials for Catalysis, edited by P Serp & J L Figueiredo, (John Wiley & Sons, New Jersey, USA) 2009, Chap. 13, pp. 481-506.
133. Park J H, Kim S & Bard A J, Nano Lett, 6 (2006) 24.
134. Dai K, Peng T, Ke D & Wei B, Nanotechnol, 20 (2009) 125603.
135. Xia X-H, Jia Z-J, Yu Y, Liang Y, Wang Z & Ma L-L, Carbon, 45 (2007) 717.
136. Ou Y, Lin J, Fang S & Liao D, Chem Phys Lett, 429 (2009) 199.
137. Guldi D M & Prato M, Acc Chem Res, 33 (2000) 695.
138. Gust D, Moore T A & Moore A L, J Photochem Photobiol B, 58 (2000) 63.
139. Makarova T, Semiconductors, 35 (2001) 243.
140. Apostolopoulou V, Vakros J, Kordulis C & Lycourghiotis A, Colloids Surf A, 349 (2009) 189.
141. Xie Q, Perez-Cordero E & Echegoyen L, J Am Chem Soc (1992) 3978.
142. Ohsawa Y & Saji T, J Chem Soc Chem Commun, 10 (1992) 781.
143. Kamat P V, Bedja I & Hotchandani S, J Phys Chem, 98 (1994) 9137.
144. Kamat P V, Gevaert M & Vinodgopal K, J Phys Chem B, 101 (1997) 4422.
145. Krishna V, Noguchi N, Koopman B & Moudgil B, J Colloid Interface Sci, 304 (2006) 166.
146. Krishna V, Yanes D, Imaram W, Angerhofer A, Koopman B & Moudgil B, Appl Catal B, 79 (2008) 376.
147. Kamat P V, J Phys Chem Lett, 1 (2009) 520.
148. Lightcap I V, Kosel T H & Kamat P V, Nano Lett, 10 (2010) 577.
149. Hernandez Y, Nicolosi V, Lotya M, Blighe F M, Sun Z, De S, Mcgovern T, Holland B, Byrne M, Gun'ko Y K, Boland J J, Niraj P, Duesberg G, Krishnamurthy S, Goodhue R, Hutchison J, Scardaci V, Ferrari A C & Coleman J N, Nat Nanotechnol, 9 (2008) 563.
150. Williams G, Seger B & Kamat P V, ACS Nano, 2 (2008) 1487.
151. Gómez-Navarro C, Meyer J C, Sundaram R S, Chuvilin A, Kurasch S, Burghard M, Kern K & Kaiser U, Nano Lett, 10 (2010) 1144.
152. Liang Y T, Vijayan B K, Gray K A & Hersam M C, Nano Lett, 11 (2011) 2865.
153. Cao L, Sahu S, Anilkumar P, Bunker C E, Xu J, Fernando K A S, Wang P, Guliants E A, Tackett K N & Sun Y, J Am Chem Soc, 133 (2011) 4754.
154. Aprile C, Corma A & Garcia H, Phys Chem Chem Phys, 10 (2008) 769.
155. Anpo M, Yamashita H, Ichihashi Y, Fujii Y & Honda M, J Phys Chem B,101 (1997) 2632.
156. Zhang J, Hu Y, Matsuoka M, Yamashita H, Minagawa M, Hidaka H & Anpo M, J Phys Chem B, 105 (2001) 8395.
157. Ikeue K, Yamashita H, Anpo M & Takewaki T, J Phys Chem B, 105 (2001) 8350.
158. Ikeue K, Yamashita H & Anpo M, Chem Lett, 28 (1999) 1135.
159. Anpo M, Higashimoto S & Matsuoka M, Eco Ind, 4 (1999) 11.
160. Yamashita H, Fujii Y, Ichihashi Y, Zhang S G, Ikeue K, Park D R, Koyano K, Tatsumi T & Anpo M, Catal Today, 45 (1998) 221.
161. Anpo M, Yamashita H, Ikeue K, Fujii Y, Ichihashi Y, Zhang S G, Park D R, Ehara S, Park S-E, Chang J S & Yoo J W, Stud Surf Sci Catal, 114 (1998) 177.
162. Yamashita H, Ichihashi Y, Zhang S G, Matsumura Y, Souma Y, Tatsumi T & Anpo M, Appl Surf Sci, 121/122 (1997) 305.
163. Yamashita H, Ichihashi Y, Anpo M, Hashimoto M, Louis C & Che M, J Phys Chem, 100 (1996) 16041.
164. Bossmann S H, Turro C, Schnabel C, Pokhrel M R, Payawan L M Jr, Baumeister B & Woerner M, J Phys Chem B, 105 (2001) 5374.
165. Yamashita H, Takeuchi M & Anpo M, Encyclop Nanosci Nanotechnol, 10 (2004) 639.
166. Chu S Z, Inoue S, Wada K, Li D & Suzuki J, Langmuir, 21 (2005) 8035.
167. Alvaro M, Carbonell E, Fornes V & Garcia H, Chem Phys Chem, 7 (2006) 200.
168. Wang W, Park J & Biswas P, Catal Sci Technol, 1 (2011) 593.
169. Anpo M, Yamashita H, Ikeue K, Fujii Y, Zhang S G, Ichihashi Y, Park D R, Suzuki Y, Koyano K & Tatsumi T, Catal Today, 44 (1998) 327.
170. Yamashita H, Honda M, Harada M, Ichihashi Y, Anpo M, Hirao T, Itoh N & Iwamoto N, J Phys Chem B, 102 (1998) 10707.
171. Ogawa M, Ikeue K & Anpo M, Chem Mater, 13 (2001) 2900.
172. Colmenares J C, Luque R, Campelo J M, Colmenares F, Karpi?ski Z & Romero A A, Materials, 2 (2009) 2228.
173. Tachikawa T, Fujitsuka M & Majima T, J Phys Chem C, 111 (2007) 5259.
174. Salvador P, J Appl Phys, 55 (1984) 2977.
175. Dloczik L, Ileperuma O, Lauermann I, Peter L M, Ponomarev E A, Redmond G, Shaw N J & Uhlendorf I, J Phys Chem B, 101 (1997) 10281.
176. Song C, Yu W, Zhao B, Zhang H, Tang C, Sun K, Wua X, Dong L & Yi Chen, Catal Commun, 10 (2009) 650.
177. Chen X & Mao S S, J Nanosci Nanotechnol, 6 (2006) 906.
178. Huang H, Gub X, Zhou J, Ji K, Liu H & Feng Y, Catal Commun, 11 (2009) 58.
179. Zhihuan Z, Jimin F & Zhizhong W, J Cleaner Prod, 15 (2007) 1894.
180. Shaohua L, Zhihuan Z & Zhizhong W, Photochem Photobiol Sci, 6 (2007) 695.
181. Zhao Z, Fan J, Xie M & Wang Z, J Cleaner Prod, 17 (2009) 1025.
182. Jeyalakshmi V, Mahalakshmy R, Krishnamurthy K R & Viswanathan B, 15th National Workshop on The Role of New Materials in Catalysis, NCCR, IIT Madras, Chennai, India, Dec 11-13, 2011.
183. Zou Z, Ye J & Arakawa H, Chem Phy Lett, 333 (2001) 57.
184. Ye J, Zou Z, Arakawa H, Oshikiri M, Shimoda M, Matsushita A & Shishido T, J Photochem Photobiol A Chem, 148 (2002) 79.
185. Jeyalakshmi V, Rajalakshmi K, Krishnamurthy K R & Viswanathan B, 15th National Workshop on The Role of New Materials in Catalysis, NCCR, IIT Madras, Dec 11-13, 2011.
186. Seshadri G, Lin C & Bocarsly A B, J Electroanal Chem, 372 (1994) 154.
187. Ibram Ganesh, Mater Sci Appl, 2 (2011) 1408.
188. Izumi Y, Coord Chem Rev, (2012), http://dx.doi.org/10/1016/jccr-2012-04- 018.
189. Anpo M, Yamashita H, Ichihashi Y & Ehara S, J Electroanal, 396 (1995) 21.
190. (a) Lin W, Han H & Frei H, J Phys Chem B, 108 (2004) 18269
191. (b) Ulagappan N & Frei H, J Phys Chem A, 104 (2000) 7834.
192. Yang C-C, Vernimmen J, Meynen V, Cool P & Mul G, J Catal, 284 (2011) 1.