Expressing "to be fond of" with 热衷 and 热心
The verb 热衷
热衷 
is used to express a strong interest in something.
We should use 热衷 according to the following structure to show interest in something:
is used to express a strong interest in something.
We should use 热衷 according to the following structure to show interest in something:Scheme
热衷
于
what
Examples
他们都热衷于环境问题
They are all very interested in environmental issues
tāmen dōu rèzhōng yú huánjìng wèntí
我并不真正热衷于经济
I'm not keen on economics
wǒ bìng bù zhēnzhèng rèzhōng yú jīngjì
Scheme
对
what
热衷
Examples
我对物理和化学并不太热衷
I'm not very keen on physics and chemistry
wǒ duì wùlǐ hé huàxué bìng bú tài rèzhōng
她对音乐越来越热衷
Her interest in music is growing
tā duì yīnyuè yuèláiyuè rèzhōng
The word 热心
热心 can be used either as a verb, an adjective, or a noun.
can be used either as a verb, an adjective, or a noun.As a verb
We can use 热心 as a verb to express “to be passionate about”, “to be enthusiastic about”.
Pay attention
We also can use 热衷 in the combination 热心于
Examples
你那样做真是热心公益啊！
You are so concerned about public welfare!
nǐ nàyàng zuò zhēnshi rèxīn gōngyì a
他们热心购买公债
They tend to buy government bonds
tāmen rèxīn gòumǎi gōngzhài
他是一个热心于运动的人
He's really into sports
tā shì yí ge rèxīn yú yùndòng de rén
As an adjective
热心 as an adjective means “enthusiastic”, “amiable”.
Examples
她很热心，愿意帮忙
She is very enthusiastic and willing to help
tā hěn rèxīn, yuànyì bāngmáng
她很热心地建议我试试本地的图书馆
She kindly invited me to visit the local library
tā hěn rèxīn de jiànyì wǒ shìshi běndì de túshūguǎn
As a noun
热心 as a noun means “enthusiasm”, “zeal”.
Pay attention
However, 热心 as a noun is rarely used.
Examples
我有热心，有责任心，有较强的忍耐力
I am enthusiastic, responsible, and have endurance
wǒ yǒu rèxīn, yǒu zérènxīn, yǒu jiàoqiáng de rěnnài lì
他是新来的中尉， 充满激情和热心
He is a new lieutenant, filled with enthusiasm and excitement
tā shì xīn lái de zhōngwèi, chōngmǎn jīqíng hé rèxīn
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