Dataframe index

Python Help
1 
i am importing dataframe from excell. Colmun 1 set as index. i want set zero in empty cell with for loop. it is not working
df = pd.read_excel(r'*********', header=None, index_col=1)
for i in range(1,31,1):
    if df.index[i] == 'nan':
        print('Empty')
    else:
        print('llll')